I have a 7 yr. old cat (Kedi), and got a kitten last April. It was touch & go for a couple days, then they started playing, sleeping and grooming each other.

However, at one point soon after, they would play REALLY rough with each other. Sometimes big (14 lbs) kitty would seem too tough with the little one. He would often pin the kitten (Wylie) down and bite him, etc.
It worried me at first, and everyone on the cat pages assurred me it was normal: older kitties will play with kittens like that to teach them how to defend themselves, and to hunt.
It seemed okay also because they would curl up and go to sleep with each other afterwards.

Now, Wylie is bigger than Kedi, and wins most of the 'battles'...........but they are still very close.
I call them my little 'lover-boys'