I totally disagree on this. There are remarkable physical differences between a 16 yo, and a 28yo.
Your mental capabilities are different, your hormonal level is completely different etc.
Yes, there are cultures or where teens are forced to act as adults to function in society, but that doesn't make them they have the same capabilities as of an adult, be either physical, or emotional/mental.
And, traditionally armies are staffed with 17-20 yo. Do you know why? Because they make better cannon fodder, and more likely to obey orders, take higher risks, which are correlated with the high testosterone levels that teens do have.
(BTW, I am 30, and when I was 16 I was basically acting as supervisor of a team of 12 workers when my family was building the house due to my father having heart problems. Yes, I was good with money, I could negotiate some, tell people what to do to a certain point, but I lacked emotional intelligence, tact, or general maturity to handle more finer problems).