I have grown several peach trees to fruiting age from pits. I have rarely had growing conditions that would allow the trees to set that heavily (late frosts, etc). I do thin on any tree that appears to need it, but this was not the case when I first got started. To weigh in on your particular questions I would say:

• Yes, peach trees grown from pits fruit quite soon (year three or four in my case)
• Yes, peach trees do tend to overbear. BUT, in my opinion a seedling tree "left alone" for 10 years is highly unlikely to end up disfigured from overproduction, unless "left alone" means given the utmost in growing conditions and the best climate. There are dozens of such trees that I can think of where I live (both seedling and grafted), and none of them seem to have this trouble. In fact, of those that even produce crops of peaches, none have ever grossly overproduced.

I guess the bottom line is, nature figures it out. Oh, and peaches are a very ancient fruit, but it was recently discovered that they have been modified exceedingly little from their wild state! In other words, no major genetic differences were discovered in the remains of pre-domestication peaches compared with modern ones. This cannot be said for the majority of other commonly grown domesticates.