Most of us wrestle enormously with the concept of ourselves as sexual beings. It's far easier to embrace more comforting notions that we are, first and foremost, creatures of vocation, family, intelligence – and that we can think our way out of any sexual urges that threaten our rationality and decorum.

I happen to be a person who loves good sex. I have an open-minded husband, and I believe that there's nothing wrong with allowing your children to see that you are a sexual being – as long as the glimpses they catch are appropriate ones, or at least properly explained.

How does your internal dialogue go? Would it be fair to say that you, like me, spend a fair amount of time negotiating sexual urges and implementing the necessary controls? Or perhaps, like many, you just wish you had some sexual feelings with which to contend.

There has been relatively little research into most areas of sexuality – except, of course, when someone stands to make serious money from "proving" that enough people suffer from some kind of sexual difficulty. So isn't it highly likely that personal stories, truthfully expounded, give us the most valuable insights into the nature of human sexuality in any given society?

As sexuality unfolds throughout our life span, it also fluctuates – even radically – over short or longer periods as it is influenced by changing life events, thoughts and experiences. That's why I've recorded the testimonies of men and women of various ages, who have experienced each stage of life, to tell the sexual story of our lives.

Teens and 20s

However they occur, first sexual experiences are defining moments in a person's sexual development. It's been claimed that engaging in sexual activity makes teenagers feel bad about themselves, but there's quite a bit of evidence suggesting that sexually experienced adolescents over the age of 15 actually tend to have better self-esteem than their less-experienced peers. There is, potentially, the freedom to perfect lovemaking skills in our 20s, but many are still confused or find it difficult to please a partner, while others simply cannot find one.

"I became sexually experienced out of the blue. I had left home at 16. A year and lots of travel later, I was seduced by a lovely 35-year-old divorcee. There was lots of crazy kissing and falling all over each other. She assured me I was the best she had ever had and I really believed her. I didn't tell her that she had 'taken' my virginity, because I thought she wouldn't believe me – and, if she did, she would freak out over the age difference. I was then – and remain to this day – rather good at the whole business."

"When I first had sex with a girl I was 14. My friends were pressuring me to do it, but secretly I was in a gay youth outreach programme. When I came back from one meeting, I told everyone I was gay and I was proud to say it. A lot of people were just 'duh'. I was dating a girl at the time, but we only had sex three times in a year."

"My first intercourse was with a boyfriend when I was 13. He was 16, and we had a long, loving and intensely sexual relationship. We were both curious. I seemed to have absolutely no fear or self-consciousness. It was a really beautiful time of experiencing my own body as it related to his. I had a three-year relationship with him, and it ended amicably after he went away to college."

"We had to do it standing up, when I was ostensibly taking her home at night. There were lanes with doorways and railway stations that were closed for the night – these places were known as 'knee-tremblers'. We couldn't possibly be good lovers – the object was to come as fast as possible, and before you got caught by a passerby or the police. Female orgasm didn't enter the equation. We didn't even know there was such a thing."

"We met when we were both studying in Edinburgh and in those days we'd have sex all the time – three, four times a day. But after we graduated, reality set in. There was massive competition in my law firm. I was working 14 hours a day. My partner was also working long and stressful hours in the fashion industry. All either of us wanted to do when we came home was have a couple of bevvies and fall asleep."

"It got to the point where I was in a double bind: I dared not confess that I was still a virgin, but I knew that if I took the plunge and had sex with one of my peers, they would know. Dating became enormously stressful because there was always a point where I had to decide, 'Should I trust this person with my secret and get on with it?' I was 34 when I finally threw caution to the wind. It involved a holiday in Spain, a local shopkeeper and a bottle of tequila."

"I suppose I was just lucky to have quite a number of partners (men and women) – most older and more experienced than me – each of whom taught me different things. I just loved how sex made me feel. Oh my God, when I think back to some of the things I tried – doing it in a public library, doing it with two men at the same time, being a woman's 'sex slave'. It was wild and wonderful, and I don't regret any of it for a second."

30s and 40s

Just when we thought we'd got it together – learned how to have sex with a partner, and have some idea who we are sexually – we start facing new challenges. All kinds of nemeses dampen our fire: children, elderly parents, a sense that we're not kids any more. Many people in their 30s and 40s have been in a relationship for quite a few years and are faced with the challenge of trying to keep their sex lives fresh and exciting. No wonder there's one question on many people's lips: "Is everyone having more sex than I am?"

"In my 30s I had two small children under five. Sex was the last thing on my mind. I also had elderly parents to care for and a full-time job. 'Sex? What's that?' was my feeling."

"After 14 years of being happily married, I discovered that my husband liked to cross-dress. He had been borrowing my clothing when I wasn't home, dressing up and masturbating. I wanted a divorce. I felt terribly betrayed and thought he was gay or transgendered. Fortunately, we had some counselling, which saved our marriage. It turned out he is just a heterosexual man who is turned on by female clothing – he hadn't told me because he felt ashamed. Apparently lots of men have the same fetish. I had to stop him borrowing my clothes, because he was stretching them out, but we're still together, and I even bought him men's size 11 high heels for his birthday."

"In my 30s, I felt quite desirable and sensuous. Sometimes I would make love to two different men in one day. It was the 70s, so there was the pill and IUDs – and before Aids. In those days I was pretty much run by my sexual feelings. I didn't get married until I was 48."

"I put an ad in the paper, to see if I could find a woman who would be willing to try a few things. I made it clear that being in a wheelchair meant I had a few physical limitations, but that I was finally ready to experience things I'd been missing. I was afraid I'd get a 'do-gooder', who wasn't really into it, but actually I found an amazing woman who totally shared some of my own fantasies."

"In my 40s, I realised I simply couldn't get all my needs met with just one man. So I started looking around for other men who offered things my husband failed to provide – great sex, for example. I felt guilty, but I told myself these other men actually made it possible for me to stay married."

"Men are simply not looking at me the way they used to. Oh, they still flirt with me, and we'll have a great conversation, but at the end of the evening they disappear into the night with a 20-year-old on their arm. Then I feel foolish for thinking they were interested in me, and the self-loathing sets in."

"We became 'swingers' a few years ago. We're both in our 40s, have pretty high sex drives and are open to different possibilities. We belong to a private group that organises parties – usually in a discreet suburban home. We pair off with people we're attracted to in different rooms and tell each other about it afterwards. Problems? Occasionally one of us wants to see someone we've been with again – without our spouses – but that's against our rules."

50s and 60s

New challenges may require us to work harder to maintain our sexual health. Navigating menopause, dealing with hormonal changes and having potentially serious diseases such as cancer can all affect sexuality; however, many people have fantastic sex during these decades – because they are smart enough to slow down and enjoy it more.

Whether or not younger people can accept it – and there are many prejudices about sexuality later in life – sex is extremely important to many older adults. Our sexuality can actually improve as we age.

"I suppose it might be because I no longer have issues with enjoying sex – my concerns about right or wrong, about pregnancy and about being interrupted by children are long gone – but I definitely enjoy it more and always have great orgasms. I'm much better at letting my partner know what I want, too – that didn't happen when I was younger."

"The issue for me now, in my 50s, is not so much sex but the way I feel about myself and my body, which affects my sexuality. I just don't feel so powerful as a woman because I don't have that edge of confidence in my ability to attract any man I want – how I miss that! Many of my female friends say they don't care about it any more. But I wonder if they're telling the truth."

"To be honest, I would say this is the best sexual time of my life (apart from three years at university when I was 18 to 21). My partner and I now experiment… We finally have time for sex and actually plan 'sex evenings'. We use sex aids and pornography helps! Plus there is Viagra…"

"Honestly, it's such a relief now to be beyond all that preciousness – 'Is my tummy hanging out?', 'Is my backside too large?' At one point my lover said to me, 'Look, neither of us is 25 any more – let's just enjoy ourselves!' Somehow he gave me permission to enjoy sex the way it should have been for all those years when I was judging myself – and my partner – quite unnecessarily."

"These days I mainly enjoy lazy sex. The athletic stuff was fun when I was younger, but there's just no need for all that now (was there ever?). Just lying comfortably and touching, holding, stroking – that's what does it for me."

"I married when I was a virgin nearly 50 years ago. I've been attracted to other men, but they've been married. So I've only ever had sex with one man my entire life. I'm sad about that."

"I rarely talk to my friends about their sex lives, but I get the impression that most folk my age – mid-60s – do it rather rarely. But I could be wrong; we don't discuss it. I do know that one of my husband's friends recently said to him, 'I haven't had sex in two years.' He is 'happily married'."

70s, 80s and beyond

From the discussions I've had with people in their 70s and 80s, it is clear that sexuality ranks pretty high on their list of priorities. Some may want more of it; others are actively looking for a partner. Many long for information about sexuality at their particular age, including how to navigate bodily issues that can make sexuality more challenging in later years.

"The movies are all about romance between young people. There seems to be little recognition that older people could be having the same feelings – let alone acting on them. But my friends and I – mainly single at this point – are interested in similar things, only we keep quiet about it because we don't want to shock our kids."

"There's one gentleman here in our senior residence who's quite a wolf. He chases all the ladies and doesn't want to take no for an answer. Some of the ladies flirt back, but I wouldn't want to be thought cheap."

"I still appreciate beautiful young women, and I don't care if I come into the category of 'dirty old man'. I still have those thoughts. Of course, I don't approach them – that would be asking for trouble. But looking's free, isn't it?"

"We've changed the way we do things. Once upon a time we used to have sex standing up, on the floor, on the kitchen table; now it's a soft surface and the easiest way possible. Frankly, I wouldn't say it's any less enjoyable – just less likely to cause rug burn!"

"I don't have many surviving friends who are also gay. I had a whole network – they were my world – and they all disappeared. I'm lucky my roommate survived it all. He's very interested in having sex, but his chances are diminished, too. When gay men are over 45 or 50, their problem is similar to many single women – they become invisible

"The funny thing is, I don't really notice my wife's ageing signs – wrinkles and so on. I know she's got them, but when you're with someone for years and years, you kind of see them as they always were. She's still very appealing to me."

"My life is so full I never even think about intercourse. We never talk about sex here (in the residence), unless there are three or so together in the lounge; they will chat together and say, 'You know what I heard?', then mention, 'I heard so-and-so was meeting up with so-and-so... Well, we know what they'll be doing!'."

"The details of my fantasy sex life are quite similar to what they were many years ago. In my mental pictures, I haven't aged."

• This is an edited extract from Sex Life: How Our Sexual Experiences Define Who We Are, by Dr Pamela Stephenson Connolly, to be published by Vermillion on 2 June at £20. To order a copy for £16, with free UK p&p, visit the Guardian Bookshop.