Re: Midchuck's observation that young people have only had so many years of practice:
Research has shown that certain manual musical skills can be learned up to the age of 13 or so (and improved upon with time), but if not learned by that age they will never be learned. The brain's/body's window of opportunity for acquiring these skills closes.
Furthermore, as with learning nearly anything, an early start makes a world of difference. Ten years of practice starting from eight years of age could result in more improvement than, say, 20 years of practice starting from the age of twenty-five.