How can I tell if my 5 year old cat is bothered by my 3 month old kitten chasing him or if he is playing WITH her?

I’ve a 5 year old male cat. Saturday, we brought a 3 month old female kitten in the apartment. She’s in awe of her “older brother”. She chases after him whenever she can. He’s running out of places to jump to that she can’t get to (i.e., the windowsill worked for one day, then she was able to get to it. Now his only place is on top of the treadmill. It won’t be long before she makes that too). Physically, she’s no match for him. He’s three or four times her size and all muscle. They’ve gone nose to nose many times with no problem. Funny, but she’s real cautious of my 15 year old female cat and wouldn’t THINK of chasing her.