Glad you had such a positive experience with your son. Personally, I would not put a tank on a child until he can do two things: read and understand his equipment (I.e. SPG, depth and computer) and second understand the basic physics of diving. My kids started snorkeling pretty young, and they were happy and safe with that, but certification didn’t happen until 16. If we lived in an area with 50’+ visibility, maybe 12. Just my 2psi
Most people will agree with you. Nowadays children are kept protected by many dangers, whilst 60 years ago they were left alone in the road, playing with friends without any adults supervising them, and exposed to any sort of risks. Some did not survive...
Some others, as me and my wife, survived, albeit now we understand how lucky we were. We did play with fire (literally), with explosives, with any sort of DIY vehicles, we did climb tall structures and trees, we did swim in rivers with strong current. Our parents simply did not care.
With our children we did take a different approach, we did care a lot. But we did never think to "shield" them from dangerous activities, which we enjoyed so much in our childhood. We wanted they to perform these activities, but with our strict supervision and guidance, and training them on how to do them properly.
We introduced them to "dangerous" sports since very young (because if they start before 3-5 years the risks are much smaller than starting, say, at 10-12 years, as small children obey perfectly to their parents, while when they grow up they tend to want to experiment their own approach). Our sons started skiing very early going on mountain bikes at 3 years and on small motocross motorbikes at 5 years, climbing mountains and trees, etc.
Regarding water, we never left them unsupervised. And we are quite convinced that free diving is much more dangerous than scuba diving, so we avoided almost entirely to teach them how to free dive more than one meter deep, and instead we gave them small air tanks for going deeper.
I started free diving when a child, without any guidance or training, and I risked my life several times. I was resuscitated twice after passing out at small depth. Instead I had never serious accidents while scuba diving, and I prefer to see my sons breathing calmly from their regulator instead of holding their breath for staying underwater a few seconds more (which is how I risked my life when young).
I respect the opinion of prudent parents who wait that their sons are grown up before introducing them to dangerous activities. As said, this is by far the most common choice, and often I had other parents complaining of what we were doing with our sons, saying that we were completely mad, and furthermore that we were giving a bad example to THEIR sons, who wanted to emulate our sons and also be allowed to use those nice small scuba tanks in the sea. So we have learnt to do these activities far from the public, going with our small inflatable boat in remote beaches or in caverns, where no one could complain about what we were doing.
The same with motocross bikes, doing it in public areas was causing a lot of blame from other parents, so we were going in remote locations in almost inaccessible valleys to practice our favourite extreme sports.
I know that these things are wrong for most people, and I do not expect that many other divers here on SB will agree with me that the better age for staring children to scuba is below three years.
Not all parents are the same, not all children are the same. I just reported here the peculiar case of our family, not pretending that this can be applied identically to every family.