I vote for Geocaching. There are real boxes and containers hidden all over the world. I’m willing to bet you walk or drive by at least a dozen of them every day.
You find the box, sign the logbook inside, take a small prize, and trade an item. The whole adventure is free! There is no need to give out a credit card number or sign up for a premium account.
You can play with an old GPS or a smart phone that can display GPs coordinates.
If you are really lazy you can print out the map for each cache and that will get you very close without using any with using any equipment.
Start with caches that are rated Difficulty: 1(Easy); Terrain: 1 (Very easy, wheel chair accessible.)
Take a picture of him finding the cache and he will be hooked!
Side benefit for him: Without realizing it he will gain map reading skills and a better understanding of Latitude and Longitude and how we fit on this great planet. .
Side benefit for you: Many single people do it. And generally anyone doing it: is in reasonably good shape, likes the outdoors, is somewhat tech savvy, enjoys a bit of adventure (the higher difficulty and terrain caches can be quite challenging and require teams.), and has the ambition to do something other than sitting on the couch drinking and watching TV . Anyone can write “Likes walks in the park” on a dating profile, but geocachers actually mean it and do it!
And with an account you can snoop a little, read profiles, see if they like to travel, see how they write, look at the caches they attempt. Someone who goes after 5, 5 caches (the most difficult and most dangerous requiring special equipment SCUBA, rappelling gear, etc.) will likely not be the best match for a homebody person with a casual interest.
There are regular free events you can attend with, or without, your son where you will meet people in similar situations. (I’ve gone to several events and the M:F ratio is always very close to 1 with people of all ages.)
Look it up. Watch the 75 second video and make an account. Geocaching
You’ll be glad you did.
Side bet. I will bet there are at least 4 within a 3 km radius of your house! Once you sign up you ask for alit of the closest ones. You will be surprised.