OK guys here's my two cents. At the tender age of 12 this kid (me) was entering 7th grade was flying by himself from Huntsville to Ft. Lauderdale, which we all know means a connection in Atlanta. I got off my flight from Huntsville, looked at the boards, found my flight to Ft. Lauderdale, got my gate, and went to go grab some dinner. I finished up my dinner, and headed over to my gate, I looked at it, and noticed it was flight 323 not 1415. So I go back to the boards and realized everything was hours late due to bad weather in the NYC area. So I walk up to the counter and tried to exchange my tickets, all the while trying to milk it for upgrades, free flights, etc. Needless to say I got my tickets exchanged, called my father and let him know, and made it back to FLL just 10 minutes later than I was supposed to.
Flash forward a couple of years to my 17 year old sister, senior in high school. She flew non-stop to Detroit for some Engineering confrence or whatever. On her way back she oversleeps and misses her flight. Next thing we know my mom recieves a phone call from a Northwest ticket agent with my sister sobbing in the background. The agent says there's a flight later in the day, and she'll put her on it, my Mom agrees, and that's that. But my sister didn't have the sense to figure that out herself.
What's my point here? It all depends on the person. I was far more competent at age 12 than my 17 year old sister, it just depends on how savvy the person is. I've been traveling alone almost exclusively since then, with very few exceptions.