To the instructors - Based on your experience, if he was coordinated enough to start hitting the green chairs during his second group lesson on skis, does that translate to being coordinated/developed enough to have a chance at being successful at learning to ride as a 5-year-old?
I'm an instructor, and here's my experience with other people's kids: EVERY (and that's no exageration) EVERY 5yr old I've instructed amounted to me walking up the magic carpet with them and holding their hands for the entire lesson... no chair lifts (since I can't ride one without my board). If I was fortunate enough to have a second person with me, I could point them downhill and have the second person play catcher. It was still a great experience for the kids, though. By the end of the first lesson, they all understood the concept of toeside/healside, but couldn't really execute on their own.
And my experience with my own kids: I started my twin girls when they were 5 (better than average athletes, but not supernatural). We went out at least once a week. Spent the first half of the year walking down with them and holding their hands. Second half, they were riding the chair, but I had to stay with them (their hands were too small to buckle in by themselves). They're 8 now. They ride switch like it's natural, look good on blue runs and OK on black, small jumps (about 2 feet of air) and started riding boxes this year.
My opinion: If you have the time and energy to walk with them for the first few months, it's well worth it to start them as early as they're willing