Age restrictions are placed on all manner of things in our society, both in the interests of the individual and society at large.
There are several age restrictions in sports in place already -- notably women's (girl's, really...) gymnastics, and NBA basketball. Major League Baseball expends considerable resources making sure birth certificates of young, foreign-born prospects are legitimate, as major league teams are prohibited from signing anyone under the age of 16.
If Ms. Stone somehow manages to win the US Amateur, she'll no doubt be hit up with endorsement offers and urged to turn pro by non-disinterested third parties. Does anyone on this board think that's in the best interest of any 10-year-old?
I'm not entirely sure what the appropriate age is for competition in a given sport at its highest, national or international levels. Several swimmers (some of whom I actually know) have qualified for the Olympic Trials, and thus were eligible for making an Olympic team, at age 12. And that strikes me as too young. 10 is far too young. 16? 15? Maybe. Like the late great Justic Potter Stewart, referring to what is now the internet's most profitable enterprise
, I'm not sure I can define it, but I know it when I see it. And playing the US Amateur at age 10, for me, is too young -- way too young.
Full disclosure: Two of my sons have competed at state-level championships beginning at the age of 10 (the youngest) and 12 (the oldest). But they have only competed against (and trained with) their peer groups, and have never competed beyond state-level contests. Nor would we allow it, as parents. I would never allow my 10 or 12-year-old to compete in a national championship like the US Amateur. If they are that good when they are 16 or 17, then maybe.