Teens are driving less, starting to drink alcohol later, and having sex later. Sounds good, right?

"When you have fewer teens drinking alcohol, and having sex and driving, they are going to be safer," Dr Jean Twenge, a psychologist at San Diego University, told Lateline. "Fewer of them are going get hurt."

But what might sound like progress, Dr Twenge said, may actually be indicative of larger trends that may be harming the current generation of teenagers.

Dr Twenge is one of several experts to highlight the issues confronting what she calls "iGen", the very "cautious" generation of adolescents born after 1995.

She is the lead author of a study, published on Tuesday in the journal Child Development, that suggests today's adolescents are growing up slower — indulging later than their predecessors in adult activities such as drinking, driving and having sex.

Analysing seven large surveys of 8 million American 13- to 19-year-olds between 1976 and 2016, the study suggested a broad-based cultural shift, and noted the trend may be linked to a marked increase in time spent online.

Eschewing face-to-face interaction with their peers, while delaying their entry to the workforce and looking less fondly on risky behaviour, modern adolescents may be taking longer to develop a sense of personal identity and resilience that will help them transition to adulthood, some experts believe.

And that may have repercussions for mental health.

"A big national screening study found a 50 per cent increase in clinical-level depression between 2011 and 2015," she said. "The suicide rate went up quite a bit over that same period.

"That's exactly when most people got smartphones and it moved from being something that only some people were doing to something almost all teens were doing for about six to eight hours a day."

Dr Twenge's most recent book, iGen: Why Today's Super-Connected Kids Are Growing Up Less Rebellious, More Tolerant, Less Happy — and Completely Unprepared for Adulthood — And What That Means for the Rest of Us, draws on her research and surveys of young people in America.

A portion of the book recently excerpted in The Atlantic carried the doomsday-like headline, Have Smartphones Destroyed A Generation?

Sorry, this video has expired Interview: Jean Twenge, Author ( Matt Wordsworth )

"Sure enough, teens who spend more time on their phones, and on screens, on social media, are more likely to be depressed and more likely to be unhappy," Dr Twenge told Lateline.

"So, there seems to be a link there — in both the change over time and then how teens are feeling — between smartphones and some of these mental health issues."

Resilience among young people a concern: expert

A similar trend has emerged in Australia. A joint report by Mission Australia and the Black Dog Institute, released in April and based on five years of surveys, found 1 in 4 teenagers met the criteria for having a "probable serious mental illness".

"We're seeing a definite increase in anxiety and depression and self-harm," psychologist and author Dr Michael Carr-Gregg told Lateline.

He pointed to a similar issue in Australia of delayed adulthood, in which molly-coddled young people were not being given the opportunities to build resilience.

"The capacity to be strong and overcome adversity just isn't there as much because they are not facing adversity," he said. "There is not much adversity in your bedroom."

Social media platforms like Instagram and Facebook, he said, were part of the problem.

"We know from the research that the more you look at these things the more likely you are to self-objectify and not feel yourself worthy and compare yourself to other people. It dramatically reduces your sense of self-worth and your confidence to go out and take the world by the throat and live life."

Less emphasis on personal freedom, Twenge suggests

Both experts pointed to a growing climate of isolation among teens — of the adolescent spending less time going out with friends to social events, and more time alone, communicating digitally.

Evidence for that, Dr Twenge said, was in the delaying over time of a classic teenage rite of passage: getting your drivers licence.

"For previous generations, baby boomers and Gen X-ers in particular ... that was what being 16 was all about. The second you could get that drivers licence, you went and got that drivers licence.

"That's why it was so stunning to me when this iGen young man [told me] 'I didn't get it because my parents didn't push me'. That's exactly the opposite of the attitude of previous generations of teenagers."

In Australia, a similar decline in licencing rates among young people has been noted in Victoria and New South Wales, according to Monash University lecturer in transport Alexa Delbosc.

The same is true in Australia for paid work among 15- to 19-year-olds, which has dropped from 54 per cent in 1981, according to the Australian Bureau of Statistics, to 44 per cent this year.

What can be done?

Dr Carr-Gregg said parents had a major role to play by not over-protecting their teenage children. He said parents should not be doing anything for a teenage child that he or she could do themselves.

"What we have to do as parents is allow our young people to be exposed to a little bit of adversity to build resilience," he said.

Dr Twenge said while some of these emerging trends were positive, society would need to monitor them over the next decade.

"We have to keep a careful eye that when these young people get to university, and when they get to their first jobs, they've had enough experience with independence and making their own decisions."