This document (page 12) discusses performance for juggling and lacrosse pre-test and post-instruction for various ages. Pretty interesting. A similar study on golf is definetely out there - somewhere.
Sidenotes:
Remember that someone (Yoda?) once told me that he had observed how 3-year olds would pick up a club & automatically swing it with a straight left arm and extensor action. Except the hitters, maybe. LOL
Obviuosly good or great results can be obtained with practice. But how good?
Obviously golf is the game of games played on (almost) any level, but don't give me that