You do need to mold someone from adolescence in order for them to be a founder or a hacker in their late teens and early 20's.
PG is in the business of spending very small amounts of money on in the slim hope that a few of them will be wildly successful and return hundreds of times on that original investment in a relatively short time frame. He invests in people who move to the valley and live huddled together on peanuts and ramen. Those young people are a very small and specific subset of all people who can be founders or hackers.
But Otherwise I agree with you entirely.