I do not know Tom (TMHeimer) personally, but his posts are logical and make sense. I do not believe he was advocating not allowing people to dive until they are @ 20 years old. His point was that divers have a lifetime of diving ahead of them, even starting at age 20, so there should be no big rush to put a child age 11 or 12 through a cert course. It is not that a 12 year old is incapable of learning to dive, but whether they could be the dive buddy you would want to have if you have a problem. I got my grandson Jr OW certified at age 12, and he was technically very good, but I knew that if there was a problem, it would be up to me to sort it out. If I had to do it again, I would have waited a couple more years, and I likely would have had a lighter task load while diving with him. Kids do dumb stuff under the best of circumstances, and being underwater just adds an unforgiving environment.