Hi Bill,
Not to be too obstreperous, but I guess it depends on how you define "recreational." L.A. County was spitting out scuba instructors beginning in 1955. They went on to teach "recreational " classes. Same with NAUI in 1960, PADI after that, etc...
My dad was scuba diving in 1953, breathed off B-24 Bomber O2 tanks in the 40's diving the reefs off Hawaii, and was freediving and spearfishing in the 1930s. He always considered himself a "recreational" diver because he did it for fun and food. One of my old dive buddies, now in his 80s, did lots of trips to Catalina with Mel Fisher on charter boats from Mel's Aqua Shop starting in 1953 (see below). They were all recreational divers.
https://cdnc.ucr.edu/?a=d&d=PVPN1953120 ... N--------1
If you are talking about the push-button wonders of today, I would say early/mid-70s with the advent of the At-Pac. My 2psi.
So if you want a range I'd say 1945 to 1960. If I am incorrect it is only because I was left unsupervised.
P.S. To be more accurate, since a generation is usually defined as 30 years, it would be 1945 - 1975.
Mark
"The diver who collects specimens of underwater life has fun and becomes a keen underwater observer. .. seek slow-moving or attached organisms such as corals, starfish, or shelled creatures." (Golden Guide to Scuba Diving, 1968)