You know there are other career paths besides start up, right? Is it wasted potential for someone to be a doctor for 25 years and then decide they want to pursue some idea for a new medical device? Hell, I think certain spaces could use more entrepreneurs that have spent time on the ground first - edtech is a prime example.
I don't know if OP is qualified for YC but I'd hardly call the career he describes a waste.
Yes, of course. Indeed I consider parenting and friendships better metrics of success than career.
In terms of a snap business decision, the hypothetical fifty-five year old doctor who cannot get anyone to jump off the bridge with them is probably not worth making a bet on. Between friendships and personal relationships, nobody who knows them is willing to make a leap of faith. Or the doctor is unwilling to work with someone else.
If not having a cofounder was not a known problem, things would be different. But it is a known problem. A mature adult who cannot solve it doesn't get as much slack as a kid who can't. The kid is more likely to have extenuating circumstances. The adult not really.
I don't know if OP is qualified for YC but I'd hardly call the career he describes a waste.