Cat with no social skills bothering other cats :/

my partner and I (f and m 29) recently (month and a half ago) moved in together, both of us had two cats before and now we have four all together. We have four boys (two being my bfs and one male being mine) and one girl (all spayed and neutered and slowly introduced with scenting, site swapping and positive reinforcement). The problem is my little guy is not great at cat social ques. For context he was a rescue from a hoarding situation and was taken from him mum and siblings at three weeks, and had pretty serious health stuff because of it, so until he was around five months old he wasn't socialized with other cats as he was recovering and being monitored. When I adopted him, he was 6 months old and he only interacted with dogs at the foster home as well as where I was living. I think the first time he truly interacted with another cat was when I adopted my girl when they were both almost two years old. In short he kind of has dog social skills. he gets really close really fast and wants to immediately smell butts and mouths upon meeting with play with other cats like he does with the dogs by pouncing and running around. he also doesn't seem to understand when they lay out their boundaries and he assumes it's just playing.

I do think he means well and is just excited to play but my boyfriend's cats are not having it. (he is five and my partners cats are 6 and 7 so maybe it's an age thing as well?). They constantly bap at him because they think he's attacking, get scared when he chases and now are a little on edge when he passes because of his previous outbursts of playtime (although they will still eat and play with us normally while hes around, and I'll come home to all the cats just being peaceful together so it seems like it might be excitement that mum and dad are home). He has gabapentin we use for high stress moments but haven't tried using it on him at home, and are purchasing a big cat tree fit for all of the kitties, but other than just locking my guy away in a seperate room I'm not sure what else to do when he gets like that and zeros in on one of the other boys.

any advice and tips would be appreciated! I'd love to be able to make all the kitties happy so if anyone has been in a similar boat and got through it I'd love to know what you guys found helpful