Is the older dog getting rough or aggressive? There is a difference.
Does the older dog seem agitated? Is he bearing his teeth? Nervous?
Or does he just growl a lot and pin the younger dog when they play?
It is much more likely that the older dog is just getting too rough. You could teach Leave it. (
http://www.shirleychong.com/keepers/archives/bite.txt)
Your dog might be too young to understand "Gentle", but you could try it:
-As soon as your dog gets too rough with either you or the puppy, then say, "Gentle" and remove it from the situation.
-After a minute or two, allow the dogs to play again.
-Repeat, and each time mark the command with Gentle.
-Most dogs figure it out pretty quickly.