To the extent possible, take your son to simply be around the airport, glider, powered whatever... Being in the environment is a good way to learn by osmosis and be around the people who are doing it. I was an airport kid from about 11 years old. People gave me menial tasks, and took me flying - and I learned! When it came to formal learning, I had a good understanding, and could articulate the basics. This made my primary training much more advanced training from the beginning. Indeed, my instructor let me land on my first formal lesson, 'cause some of the other pilots I'd been hanging around with, and done some flying with told him he could. So as I waited to be old enough to hold each license, I flew, and learned more advance things.
By always being around the airport and pilots, people who had planes got to know me, and provided flying opportunities. Mentor your son to be mature and agreeable around pilot people (who aren't always totally mature anyway
), and grow any opportunity which may present itself. Being a pilot requires serious dedication, and care for expensive equipment, but it also depends to some degree upon "who you know"...