I don't think that the vast majority of rockstars grow up mentally past their late teens/early twenties. They live a lifestyle that allows them to be Peter Pan forever. They can spend their days partying and doing drugs, with a manager to babysit them and handle all the adult decisions.

I still love rock and metal, and have ever since I really got into classic rock in middle school. But that makes me acutely aware as I grow older, people who seemed really smart when I was younger, seem dumber than a sack of bricks as I approach them in age.