I, too, was a Dec 1 kid and started early because I was brilliant I also went away to college when I was 17. The only age/maturity related problem I really experienced was when I was participating in a scavenger hunt and couldn't buy the "Hustler magazine from the 70s" because I was under 18 As for the social maturity aspects, it typically wasn't a problem. It's not like hanging out and dating were restricted to your class. A lot of that maturity is developed from experiences
The consistent points being made in this thread are that it is about the individual child and their maturity level. My oldest turned 5 in September. He has always been mature and articulate. People always thought he was older than he was, even when he was not even 2 yet and was speaking clearly, using logic and reason, knew a lot of the preschool things (numbers, letters, colors, shapes), was shooting baskets, hitting a pitched baseball and throwing spirals after making me run routes! He had outgrown preschool and the disinterest was showing, so we decided not to wait a year. So far, he is doing well in Kindergarten and has learned more than I expected in the last two months (yes, they actually do learn a lot in Kindergarten!) He actually sits down and works on his homework without us asking (too bad that won't last the next 12 years So far, we don't regret the move.
I don't "get" all the sports related concerns with starting early. For the most part, teams are based on age groups, not what grade you are in.
I'm curious to see how schools deal with having the entire senior class be 18 throughout their entire senior year, not just some being 18 for the final semester as it was in the past. Considering the actions of the kids I knew that were 18 during the last semester when I was in school, I think there's going to be a lot more "excused" absences than before!
"Just think of how stupid the average person is, and then realize half of them are even stupider!" -- George Carlin