My son is 4 years old and has really taken up a love for the game. At this point, I typically take him golfing at least once a week. I tee him up from the 150-yard stakes, except that he plays the par 3s from the red tees. We play every hole for him as a par 5.
We started the year doing the same thing, but from the 100-yard stakes. I had told him that when he could shoot a 45 from the 100s, we'd back up to the 150s, and he's already done that. He has the same offer now from the 150s: shoot a 45, and we'll back up to the 200s, and then to the adult tees.
Here are a few videos of his swing:
As of now, I've been handling his coaching. Right now, I think the most important thing for him is to play golf, to try to figure out how to hit a variety of shots, more than particulars of mechanics. At the same time, I know that this isn't my field of expertise, and at some point, if he continues to take this seriously, we'll likely be looking at lessons.
In your estimation, when is a good time to start looking at instruction?