See the history of our world championship and the ranking at the last Worlds. But Brasil, France, Holland and the Scandinavian countries almost always produce good results. And there are many cases of outstanding sailors coming from other countries. Hours spent racing and coaches who can get the best from the kids. In all three countries there are big regattas almost every weekend.
Most countries start at eight years old.
But there are plenty who start earlier and eleven or twelve is not too late - even to get to the top in the Optimist. It depends what you mean by racing. Sailors are permitted to enter the Optimist Worlds and other big regattas until the are 16, i.e. until and including the year in which they have their 16th birthday. But some sailors do get too big before then. A lot depends on local conditions, particularly during the summer holidays.