In response to OatesCam's comment:
No, it's not flat out wrong. Saying a player is good enough for an older group does not mean they are too good for their own age group. There are examples of players who have played with older players and succeded. There are countless examples of exceptional hockey talents who were placed in advanced age groups and were not mature enough for it. We talk about rushing players to the NHL causing failure all the time - the problem is greatly magnified when you are talking about children.
My fundamental point in that post is, however, simply that players are not hurt by playing with their own age group. Gretzky and other may have continued to excel playing with older kids, but my feeling is that they would have developed just fine if they were not rushed. In your specific examples, Gretz played Junior B, not major junior, as a 15 year old, and I think Eric Lindros would have been much better off if he were allowed to grow up more in his youth and not rushed along. I don't think he was ever mentally ready for the NHL and adult life in general (his neighbours today say he still acts like a 40 year old child).
And no, I don't think the choice should belong with the child an their parents. Are we going to allow 14 year olds? Really big and talented 9 year olds? Lots of kids and parents lack good judgement. Maybe you would be OK with your 15 year old son or daughter living and working and hanging out with 20 year olds. I would not. I think the league should protect 15 year olds whose parents are too star struck by the idea of their kid being the next Crosby to show good judgement.
Sorry Oates but when you make a statement like that I'm going to need you to provide some examples of players who were rushed into junior too early and suffered as a result. Those players I mentioned that had success were just a few of many but I can't think of too many whose development was stunted. Also, I disagree with your assertion that parents need to be saved from themselves regarding how they raise their kids. Just because it's not how you'd raise your kid doesn't make it wrong. The whole age group/maturity thing doesn't fly with me. Some kids are exceptionally advanced for their age. Why should a kid who thinks the game at an advanced level be treated so differently than say a chess or musical prodigy? Not all kids are the same so I don't see the point in trying to paint them all with the same brush.