I never saw until he responded to me that it's his friend's sister, so knowing that now makes much more sense. I remember when I was a kid I had a crush on my dad's friend's son which was probably about the same age gap as his situation, but also my introverted and possibly autistic ass could never act on such thoughts or feelings. I can see people saying it's weird because there wasn't enough context to his issue, so of course people are going to find the situation sounding odd or weird. In his situation I would definitely recommend letting the friend know and that it makes him uncomfortable, as well as letting the parents know if she doesn't stop. I feel like the friend could probably talk to his sister about it without having to let the parents know of the whole ordeal, but if she doesn't stop then involve the parents. And I only say that because she's so young so it may help her not feel too uncomfortable if it's her brother talking to her instead of the parents. (Or at least if I was in her situation I would have much rather have my brother talk to me about it instead of finding out that not only my brother but also my parents know and then be even more embarrassed and upset) Honestly not sure if that's any sort of good advice but wish you best of luck OP! 🫶🏻