But her son - very like both his parents - is *deeply* motivated by competition. Any kind of school work, homework, project, artistic endeavour, even play activities - frame it in a competitive way and he enthusiastically gives it his all, wants to work hard, learn more, engage more. Take away the competitive element and blah. He's checked out and half-hearted at best. My DS, in contrast, loathes any possible hint of competition, and thrives only when it's not there.
I see a parallel here with my kids and piano. My DS10 would represent the competitive version - he's motivated by recitals and will practice with a recital in mind even though it's not coming up for months. DD12, on the other hand, has always been motivated by the music and saw recitals as a necessary evil. She'll be lit from within by a song that she loves and practice it happily, but has to be dragged up on to the recital stage. They've always been like this - it's a reflection of their temperaments rather than their ages.
So I'd say it should be assessed on a child-by-child basis. First, is the child motivated and inspired by competing, and second, how does the child handle defeat? If those two aspects are healthy and appropriate, then age isn't as much of a factor.