Our society places a great deal of priority on preserving precious childhoods as long as possible. I wrote about some of its effects in Too much education? and Your Mom was right: It pays to practice.
Others have written about it, too. Like, Is 25 the new 15? (HT: Instapundit). I believe so. Which means 15 is the new 5, or maybe 8. When my nephew turned 13, I told him that he was just two years younger than his grandpa was when he decided to move 8 hours away from home to a bigger city to get a job and be on his own for the rest of his life. This was a bit of a shock. It would have been to me at 13, as well. Or 15 and 18.
Instapundit, himself thought so back in 2002.