Kid, once you get older you will find there are grown adults that have relationships together that have the entirety of your current life as an age gap. I knew a couple that had a 15 yr difference. Both adults. I have seen both male and female have been in the older spot. A mere 2 yr difference is nothing to notice. It only feels like so much because you are so young.

Also, since he is barely older than her, it is not grooming. They are both teens, and started as young teens, let them be.

Now grooming is real, and I can say I have seen that, and I am glad that young woman is out of that relationship. Speaking of, how does he treat your sister? Like an equal and a friend, or does he have no reguard for her? If he respects her, then there might be a problem