The other caveat is that you need that much practice to become an "expert". It's not clear to me exactly what "expert" means, but it can't be relative to others because others could just as easily put in 10,000 hours of deliberate practice.

So at the end of all this, he could end up a magnificent golfer, but still not win any PGA tours because the other golfers there are also magnificent players. I still have high hopes for him, though, and can't wait to see how it ends up!