> My motivation died around 30 (34 now) once I realized I wasn't going to make any kind of impact on humanity.

Seeing your confidence in that outlook, if you permit me an intrusion, I'd go so far as to say, you probably could say "decided" instead of "realized" and it would be accurate.

There are decades ahead for most people at that age. And instead of starting from scratch like an infant, you already have a lot of things going for you. If you were a close friend, I'd have badgered you relentlessly to believe in yourself. I hope as an internet stranger, I can plant a seed of belief in your mind.

Most people are capable of far more than they believe. Good luck!