NTA. My partner and I are the same ages as you and yours, with me being the younger. Her comment is ridiculous and insulting. I was 23 and my partner 29 when we met. I’m not femme but I’m not a “traditional” butch like my partner presents and I’m smaller than her etc. and literally none of my friends or family think that she was predatory.

We’re in the about the same stage of life as our partners. It’s not creepy at all. We were both consenting adults in our 20s when we met, as were you and your partner. If you were 16 and she was 22 that’d be different, but you’re not. Your cousin can be respectful of your relationship or she can stay banned.