Older rat is entirely uninterested in new rats?

I mean this is better then him being aggressive, so I'm grateful for that. But yeah I have an older boy (around 9 months old) and I recently got him two new friends.

The friends are about two months old, since someone told me it's easier to introduce baby rats since there less of a territorial threat. There two bonded rats from the same litter.

Introductions went.. well? My older boy just entirely ignored the baby's, even when they tried to climb on him. So I decided to try to put them in the same cage, and same thing.

My older boy ignoring the baby's, actively running away from them and one of the baby's trying to chase him.

The baby that was chasing him did eventually get tackled and they fought a bit, but it was short and there's no blood or screaming. I'm guessing my older boy was just trying to tell the baby to leave him alone.

On the other hand, the baby that was also ignoring him got left alone. They actually seemed to start exploring together.

My older boy has just been sleeping in his hammock while his new baby friends are exploring the cage. They seem terrified, but their feeder rats and they don't know me so that's expected. Other then that, no interactions. I'm not sure if that's a good or bad sign.

Older boy is still calm around me and begs for attention and to be let out of the cage. So no real changes in behavior.