If he's had negative experiences with older kids that would be all the more reason in my opinion to pursue that option. It isn't a healthy thing for a person to walk around believing whole categories of people (teenagers, athletic people, etc.) are unkind. That isn't to say I'd pick any random stranger but I would start talking it up with friends and be open for opportunities.
Spending time quarterbacking the past kind of puts you in control of feeling like you are doing something but in reality it won't improve the present. A huge percentage of births in this country now include induced labor and I'd hardly suggest all of those women are to blame or deserving of having disabled kids. I understand the temptation to look for an answer in the past but I'd keep a close on it because too much of that can be a sign of depression.
Many insurance plans won't pay for sensory therapy, but most will pay for kids who have hypotonia or more significant motor disabilities. It may take some fighting as insurance will sometimes initially deny claims that eventually they will pay. Usually the office staff at clinics should have good ideas for how to code and submit claims to get them paid. That said, again in our experience other activities (karate, swimming, horseback riding) accomplish as much or more than OT or PT for hypotonia. With all of it I would be realistic though and aim for improving the quality of life he has with some acceptance that not everyone is dealt the same hand.
