Mark, I’m going to go against the grain here.
You are his father. It is your job, nee your God given right, to bring him back down to earth.
Firstly, you need to ask him was it in official competition? If it’s not in a competition, then it’s not an official hole in one.
Secondly, you need to place ethical guilt on him by saying he didn’t play the hole in the spirit of how the hole was meant to be played.
Thirdly, you need to drop comments like, “Well done, but shame it wasn’t on a real course.”
These methods will work well and what’s more, by the time he needs a psychiatrist he will be over 21 and will have to pay the bills himself.
I hope I have helped.
Good response, in keeping with the spirit of this website.
Here's my thinking. If I get a "hole in one" and don't win a new car or whatever for it, who cares? I've never had one. I have a friend who says he's had seven. I really don't care and don't think more or less of him as a golfer because he's had seven. I witnessed a friend of mine make one, his third, he said. Momentary excitement, and then, so what?
Recently I came as close as I have ever come, playing by myself. The ball stopped virtually on the lip of the cup. The only witness other than myself was a guy mowing the grass. We had a good laugh about it. What if the ball had gone in and there had been no witness other than myself? The convention I hear is that if there is no other witness, it doesn't count -- it would not be "official". But, I would count it myself, for what that's worth, which would only be the fun of having it happen at the moment. I wouldn't expect anyone else to care about it, one way or the other. So, if the young man is happy that he's made a "hole-in-one," so be it. It's done.
As an aside, on the witness issue (if it is an issue), in golf we are expected to report rules violations on ourselves even if no one else sees them. Why then can't we claim holes-in-one that no one else witnesses. It seems like a fair trade to me.