I am a life-long player and evangelist for bridge, who has enjoyed success at many levels of play from tournaments to kitchens. Like your son, I learned the basics of bridge at 6 or 7 (in my case from Goren's AutoBridge), but went another 10 years before encountering a group of like-minded individuals in high school.
A major obstacle IMHO to wider acceptance of bridge (in North America - it is thriving in other parts of the world) is the perceived need to play the full current game as invented by Vanderbilt. Bridge (meaning Auction Bridge and Plafonde and other variations including Auction Whist and Contract Whist) was already a mass phenomenon before Vanderbilt's new Contract scoring table. The ability to gradually step up to more challenging variations of the game may have been a key driver of Bridge's popular success from the '30's through the '60's.
I suggest playing not just Contract Bridge with your son, but exposing him to whichever variation is playable by the opponents at hand. Play a Whist variant with less serious players from your group; play Auction Bridge with opponents interested in a slightly greater challenge, and wait to see if any of your regular group decides to step up to Contract. Play 9-5-2 Whist when three people are waiting for a fourth to show up.
Play some Poker, to help your son learn the elements of bluffing both as allowed, and as not allowed, in Bridge, so he can better distinguish them. Play some Rummy to work on his card memory.
Oswald Jacoby and Howard Schenken were not only amongst the very top world-class bridge players of their time, but also widely regarded as the best Backgammon and Gin Rummy players, respectively of their generation. While I believe Bridge to be a more multi-dimensional game than either of these, both of these will strengthen specific aspects of your son's bridge playing.
If need be, play simple Hearts or one of the many German-derived trick-taking games described in any good Hoyle. All of these games will teach your son card-playing skills that carry over well to Contract Bridge. The opportunity to observe opponents in these many different, yet similar< environments will encourage card-reading, and opponent-reading skill development by your son. All the top players are amazing technicians, but the very best have an ability to read opponents that is often uncanny, and which I believe comes from exposure to opponents in wider circumstances than just the Contract Bridge table.
But above all, play a card game.
Talleyrand, on observing 4 young women who refused to learn Whist:
What a sorry old age you are preparing for yourselves.