Why is using ''old age'' a common method manipulative men use to make you stay?

I was 34 when I finally broke up with my toxic, money hungry ex boyfriend. Ever since I've found someone and now it's been 5 months.

I've read other stories of men that tried to make the woman stay by throwing the ''but you're 30+ now, you'll never find better, you just hit the wall'' old age card.

Lets say in the worst case scenario where I didn't find anyone else after dumping him; well at least I got my mental wellbeing, dignity and self-respect back. Like those men in the stories, my ex boyfriend threw me the ''You finding someone else, someone better, LMAO (he was laughing so hard), you're now 34. I''ll give it a year. LOL, LOL''.
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I don't mean to brag but this is a coincidence:
After dumping him, I've gotten hit on by other men and I met my current boyfriend right in my Judo classes. I've been looking much younger than before. A couple people think I'm still in my 20's.
Why is using ''old age'' a common method manipulative men use to make you stay?
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