Some people are forced into an adult mindset earlier than others. I've known 14 and 16 year olds that could be trusted with more responsibility than most 30 yea

Some people are forced into an adult mindset earlier than others. I've known 14 and 16 year olds that could be trusted with more responsibility than most 30 year olds. I've also met 60 year olds with a child's mindset. Clearly, age doesn't cause maturity, but it's certainly correlated with it. An outlier can't be treated like the center of a distribution. Your own experiences don't mean that most 18 year olds aren't still children. It's not like the government is going to start maturity-testing people to decide when to start dispensing a basic income. They're more likely to test a "representative population" and set the age to the point where 2/3 test as "adult", or use one of the traditional age-cutoffs like 18, 21, or 25.