Having been denied all birthday celebrations until I left home at 16, I was always determined to mark subsequent birthdays well. I’d go to bed the night before in a juvenile state of anticipation and wake up ecstatic that I had survived another year, that I had proved them wrong and outrun the apocalypse. You see, I was brought up as a Jehovah’s Witness and believed I would die in 1976 when Armageddon came. I would never reach 30, 40 or 50 so I thought. So each birthday has been a shaken fist at the heavens well as a celebration.

My 21st lasted three days: drink, drugs, dance and a very long sleep. I came to and felt I’d finally put the cruel denials to bed and maybe that a three-day party would last me a lifetime. But I had a party for my 30th, 40th and 50th. OK, not three days long but a bit of a bash that welcomed in the next decade. So far, so good. And next year I will be 60. I thought the prospect would feel the same. That I would sashay up to the date, throw my arms out and say “welcome” as I had to all the others. But this one feels different.

Yes, I will flip from middle age to old age, but I may also flip from the Fuck-it Fifties to the Savour-it Sixties

I’ve been getting away with the term “middle age” since I turned 40. I assumed it started around then and ended at 55. Then I got to 55. I extended it, obviously. But it has to end. Next year, I can’t be middle aged any more. I must officially be old.

I think of the other 60-year-olds I have known. My mother – worn down by housework and an unhappy marriage, frightened into righteousness by an oppressive religion – was definitely old at 60 and my father was dead at 68. Aunts and uncles and teachers and people I worked for were impossibly ancient at 60, they dressed in beige and had Velcro shoes and all seemed to smell of Vicks VapoRub. I know I will never be like that. But as it gets nearer I realise I will be entering into another realm, old age, the other tick box that is 59-plus. There’s never anything after 59, you are lumped in with the 70- and 80-year-olds as though we all think the same despite a possible 30-year age gap between us.

At 60 I will be sent (my older sister assures me) a free bowel cancer check kit complete with a mini scoop to stick in your shit and send off in the post. I will get free prescriptions and eye tests. I think I get reduced admission to my local gym and a rail travel discount card. So even if you are unwilling to accept 60 and bury your head in the sand; even if, like me, you are determined to see it as just another number, the world conspires to tell you that things have changed. And at least for me, they have.

My 50s have been wonderful. I’ve become single and have had some great dates. I’m open to a new relationship, to flirting, to being wanted and sexual and expansive. I’ve found professional success writing books and essays, editing, teaching and encouraging other writers. I have used my voice to say what I think on behalf of working-class writers and marginalised people, and I’ve discovered in the Fuck-it Fifties that I truly do love myself with no apology or codicil. I have stopped looking for universal approval, worrying about fitting in and whether or not I wear, eat, read or say the right thing. But all that has come at a cost. I’ve been told I appear self-contained and intimidating, “fierce” is a word often used to describe me, all of which I find baffling.

Far from being just another decade, I think 60 might be a turning point. Yes, I will flip from middle age to old age, but I may also flip from the Fuck-it Fifties to the Savour-it Sixties. Will I slow down? Will I soften round the edges? I have noticed I am already consolidating important friendships and sloughing off those that have become negative or “taking”, which is the only word I can think of to describe them. I hope to always be making new friends, and in my 60s there may be more time for that.

There is, of course, the inevitable express train of time, hurtling away from you as you age. As 60 approaches, I do have the sense of time running out, or at the very least becoming more precious, which is the most cliched of all cliches but nevertheless true. I thought coming up to 60 would feel like just another birthday, but as it approaches I realise I was wrong. It does feel like something is about to end, and so, of course, something is about to begin.

• Kit de Waal is an author. Her latest book is Becoming Dinah