Is this weird or am I being a prude?

So my brother is dating an older woman, which is no surprise to me. He prefers older women because he's a man child and they tend to be more motherly towards him than women his own age that expect him to grow the fuck up and get his life sorted. But her age is a bit bothersome to me, but not as much as the fact that she was our lunch lady in high school.

My brother is only a year older than me, and his gf's oldest child was one grade below mine. She was my friend's cheerleading coach as well. I find the whole thing extremely disturbing since it was someone that worked at the school we went to, while we were there, and had a child only one grade below us. If she didn't work at our school I don't think I would have as much of an issue with it. But I can't get past that she keeps talking about all the kids she took under her wing and cared for at the school that were around my age while simultaneously dating one now.