You're not saying anything that argues my point. In fact, everything you stated supports my point. In saying that there's something wrong with the phrase "21-year-old kid", I wasn't saying that there are NONE. I was saying that there is something wrong with someone who is 21 years old and is still acting like a kid, and there's something wrong with someone who thinks that society shouldn't expect 21 year olds on the whole to behave like adults.
As evidence, you cite an experience where young adults acted like kids because they were actually criminals. That means they are outside the norm of behavior so much so that society condemns their behavior and puts them in confinement away from the rest of society because of their behavior. So, that supports my opinion that 21 year olds should not be expected to act like kids. For one, it can be dangerous to society in its extreme cases.
In the case of Davenport, you say it's no big deal because the team can just hire someone to watch over him. I don't disagree with that. However, it doesn't change my statement that I'm sure it's not what the team wanted or expected out of a million dollar double first round pick, not at all. Case in point, if they did expect that kind of unprofessional kidlike behavior, they would have put a "babysitter" on him from the beginning and not waited until he pissed away half the season. Further, if they expected this kind of behavior from him, I'm sure they wouldn't have drafted the guy in the first round and given up next year's first round for the privilege.