Is 18 months too early to start potty training a boy?

Sounds like he is starting to learn that he doesn't want that diaper on. My son started to potty train early. I just asked him every 10 minutes through out the day if he had to go potty. Even took him in to the bathroom and sat him on his potty chair some times he went sometimes not. He will get the ideal after a few weeks of going in the potty and learning that feeling that he gets right before he goes. Just make sure you give him lots of praise when he does go. Yes buy the potty now, but do not leave it in the living room. Take it to the bathroom so he know that is where your supposed go potty. It will be a slow process at first but once he gets the hang of it it will go easier.