Kind lady is right, there would be fur everywhere and sereious noise if they were really fighting.
There may be an element of hierarchy being established, the older cat just making sure the whipper-snapper knows his place. As your youngster grows, and tries his hand, the older cat may make his presence and status felt a little more forcefullly. It's nothing to worry about, cats are pack animals, someone has to be 'top cat' and the rest will always try to topple him now and again. In domestic situations, this is normally dealt with by a bit of sabre-rattling in cat terms - spitting, a little chasing and so on - just leave them to get on with it, unless one is seriously bullying the other, in which case you may need to look at separating them. This is very rare, so enjoy your cats, and let them enjoy each other.