Not to diminish the question; I think it is an interesting thought experiment, but thr conditions set in this are immensely subjective.

Are we saying capable as in theoretically could have the ability to contribute workforce or are currently contributing workforce? How do we say what thriving means? I’m assuming when you say living you mean reach wome standard of living and not just exclusively surviving etc.

In a theoretical/fair world probably around 98% of people 30+ can support themselves, exclusing the few people who are sick or mentally disabled. In our current world that number is significantly lower, but that is a result of structural/political issues, not if the individual peoples capabilities.