There is no clearly defined point when a person goes from being an adolescent to becoming a man or a woman. The puberty process starts somewhere around twelve or thirteen and causes a person to reach physical maturity; when a person’s body stops growing and they develop the ability to reproduce.
But intellectual and emotional maturity are something entirely different.
The only things significant about these numbers are the associations we make with them.
Specifically, the expectations we have when someone turns those ages. And certain milestones that a person typically achieves and responsibilities they are given around those times.
Eighteen is the legal age of adulthood for most things in the USA. The age a person can: vote, serve jury duty, enlist or be drafted into the military, have consensual sex with another person also aged eighteen or older, marry without parental permission, donate blood, donate reproductive material, buy tobacco products, get tattoos or piercings without parental consent, sign a hotel, house or apartment lease, sign or file legal documents and contracts, apply for insurance and government assistance, have a full time job, open a 401 K retirement account, own a vehicle, live on their own, change their name, buy a lotto ticket, gamble at a casino, buy or lease adult movies, buy a rifle or shotgun, get a credit card and checking account, can sue or be sued and will be tried as an adult for a crime.
It’s also typically the age the most have completed high school/ GED, attend college, have a job, have a driver’s license, have a car and have some idea of what kind of person they are and have at least a pretty good idea of what they don’t want to do with their life.
But as nearly everyone can attest, the age eighteen is more a doorway into adulthood rather than the final destination. A person’s life experience is still pretty limited. They haven’t “lived” much and their track record for being responsible and reliable is still suspect.
So while they are trusted to make many major decisions in their own life, it is still a full three years later at age twenty-one before they’re legally able to: buy alcohol, drive with a student driver, conceal and carry a gun or knife, buy and register a machine gun/ assault rifle, get a job as a police officer or as a federal or state investigatory agency or get a commercial drivers license (bus, limousine, semi-truck etc.).
It’s an additional four years, at the age of twenty-five when a person can finally: legally rent a car and adopt a child. This is typically also the minimum age of most degree requiring careers, such as to practice medicine or law or serve on a public education board.
But just because the law allows citizens certain rights at certain ages, doesn’t necessarily mean that people are actually achieving these milestones and becoming mature, responsible adults.
Maturity = Knowing who you are, what you want and how to get it.
Responsible = Being accountable for your decisions, being reliable and having the self-control and self-discipline to accomplish what you are entrusted to do.
There should be another list of milestones that people use to achieve certain goals. It would certainly accelerate the time it takes for a person to become a mature, responsible adult. And as anyone who has reach or passed the age of forty would attest, they could have accomplished more and obtained more success and satisfaction before their mid-life if they’d been more mature sooner.
The expression “Youth is wasted on the young” is only understood by those who have lost their youth and finally have the maturity to know who they are, what they want and how to go about getting it, but now are too old to make good use of it.