Welcome to the site. You have found your people 
You said about your son, “My hope is he gets to be the person i might have been.”
I was a little sad when you said this. Not because you should have been something else, but because you feel your too old to get what you want out of life. You still can be the person you are meant to be. Life doesn’t end at 18 or heck, even 30. Some people actually believe it begins at 40 (me crossing my fingers, I hope so; I’m 39).
Now that you’ve got the ADD under your control, learn about the good parts of it and figure out who it is you want to be and what it is you want to do with your life. It’s never too late. Maybe you can use your experience, making it into something good. Own the ADD, and your childhood. Our experiences make us who we are, and we aren’t done growing into that person we are supposed to be, ever.
Yes, it definitely has bad points, but don’t focus on those so much. It’s your chance to start fresh. Focusing on how ADD makes you an exciting, vibrant, interesting person would be better. Focus on how your lack of good common sense maybe opened up some doors, however accidentally, because you weren’t afraid to charge into things. For example, your ADD may have not let you focus on and finish the three majors, but in the end, you have a broader sense of science than most people, having studied all three. In some science or “techie” type jobs, I bet you are quite employable.
As for schooling, it’s never too late (we had a friend who was 80 when she graduated from The University of OK. She lived to be 106, so she was able to use her degree). Maybe now that you can focus, pick one of those three things and go back and get that degree. There’s no harm in learning more, right?
Good luck to you. I hope to see you around in the forums. This was a great post, thanks for sharing