7 year old cat starting to growl at kitten after a year?

I have a 7 year old neutered male cat(MJ), and almost a year ago we brought home a male kitten(SAL)and he is also now neutered. at first mj didnt care much for him, them they began cuddling on the cat tree together, playing together, and eating together. i thought they were getting along great. Now, after almost a year of being in the same house (both are indoors), MJ has started to growl at Sal. the kitten doesnt even do anything to MJ, Sal can just walk into a room that MJ is in, he'll growl, and if the kitten walks past him, Mj will swat at him.. Am I going to have to get rid of the kitten? or is Mj just getting old and agressive?