This might be a little off topic.

During the late 50's, my introduction to shooting was at 4 years old with a Mossberg 22 bolt action that I was allowed to shoot in the basement ROTC range at a large metropolitan High School my retired grandfather was a night watchman at. Sometimes, we transported my rifle and his in gun cases using the city bus system (my grandfather did not own a car). During our hour long ride, involving several bus transfers, no other passengers ever indicated the slightest sense of uneasiness.

At the age of 5, I was allowed to shoot my father's Colt Woodsman Match Target, under tighter supervision.

I think your handgun purchase should be influenced by the size of your son's hands along with his personal preference.

I have relatively small hands; the Colt shot well but was never particularly comfortable. I also have short arms; the Winchester Model 12 (with 14.5 inch stock) I began trap shooting and hunting with at the age of eight never fit me and I actually never grew into it.

The first handgun I paid for (during my teen's) was a Ruger Single Six. Although I enjoyed shooting the revolver, if I could go back in time I would have purchased a S&W 22/32. If I had paid a little extra and purchased the S&W, I'd still be using it on a regular basis today. I would have appreciated the better fit to my hands, the much quicker reloads, and the double action capability (I believe learning to shoot double action revolvers resulted in significant improvements in my shooting with any of the other firearms I have used).

Although I have "grown into" most rifles, K/L frame revolvers, and single stack semi autos, I still struggle a little for a good fit with N frames, double column pistols and shotguns with standard stock length. I'd like to think that I would be a much better shooter today if I had not spent many of my younger days shooting poorly fitted firearms.