What do you consider adolescence? Most of us would say it ends after high school, but some say we should think about it beyond that milestone. A group of researchers suggested the range should be extended to age 24 — which for many is past college age — in an opinion piece recently published in the Lancet Child & Adolescent Health.

The concept of extended adolescence is not new, given how society has changed through the years. Shifting the definition could impact social policies to support young adults, but saying adulthood starts at 25 could have unintended consequences, as well.

On one hand, I agree that young people, age 18 to 25, shouldn't be lumped into the current broad "adult" category of 18 to 65 years. I wholeheartedly support the provision that keeps children eligible until age 26 for coverage under their parents' health insurance plans. This provision is especially important for mental-health services. People in late adolescence tend to be very healthy physically, yet highly susceptible to mental-health concerns. They often don't get the care they need. So this aspect of policy regarding "delayed or extended adolescence" has my absolute approval.

On the other hand, I disagree that as a society we should accept a sweeping notion that adulthood doesn't begin until age 25. It's not helpful to our young people. In fact, I'd argue that it would tend to lower our expectations for them, lower their expectations for themselves, and, subsequently, lower their performance. As physicians, we recognize the fact that the brain is still developing in the early 20s. It doesn't stop there, however, as we continue to develop throughout life. It's not as if your brain is done changing at 25.

It does seem harder to get established as a young person in the modern era. The difference today versus 30 or 40 years ago is that well-paying jobs often require higher education. Young people today are going to college and graduate school in record numbers. Many carry significant student loan debt and they may struggle to live independently, coming out of school with that burden.

Theoretically, the more education you get, the better your job prospects. But it doesn't always work out,  and having parents to fall back on temporarily can be a tremendous help. Those who enter the workforce after high school often need help getting launched. But there's a big difference between a 22-year-old who needs a little support until she finds her feet and a 35-year-old whose parents are still paying the rent because she's made poor decisions.

Many parents provide financial help for their adult kids, and there's nothing wrong with this. The danger is the extent of the help and how long it lasts. I work with parents of young adults and I know it's hard to resist the urge to make life easier for them. Nevertheless, it's wise to instill in children the value of goal setting and working hard for what they want. Working doesn't necessarily have to be at a paying job, it could be contributing to the household.

Societal norms are shifting. People are marrying later, having children later — perhaps because they're more focused on career and education. While society has changed, our bodies have not, and a woman's fertility starts to decrease at age 30.  Unfortunately, extending the definition of adolescence does not prolong the peak childbearing years.

My advice to parents is to encourage goal setting with your young-adult children and make it part of an ongoing conversation as they mature. Often you'll find that your kids have goals and need help achieving them. Offer that help while urging them to challenge themselves in thinking about their future. Offer more than a place to stay. Provide connections to others who you think can benefit them on their journey. And know that financial support for adult children is not a bad thing — the trick is to avoid stunting their "growth" while doing so.

Miller is in the Division of Adolescent Medicine and Pediatric Gynecology at Nemours/Alfred I. duPont Hospital for Children.