What's made him decide he wants a bio child now and pick a woman your age with 3 kids already?
I'm not sure he's serious about wanting to be a father. If you really like him and he's a good man, have a conversation to check he isn't getting swept away the prospect of a last chance saloon family of his own without a significantly younger partner, which may be something he doesn't particularly want.
It may be more of a passing regret/ what if playing out. I would acknowledge this as a possibility with him, see what he says.
If he's adamant, no, he definitely wants a baby, now for whatever reason and not in the past 25 years then both sleep on it but end the relationship.
I suspect he may be back but let him figure it out, not you. If your childbearing days are over, don't get pulled into conversations about IVF, adoption. Etc. It needs to be a clear 'no'. Your circumstances are as they are, he can stay with you or move on. Don't try to make another child fit if that isn't what you want and would probably be very difficult. If it's regret about missing his chance, perhaps suggest community input but don't do the thinking for him.