I do think the younger ones pee more often but your's sounds like he's marking. I have a 1 1/2 yr old male, Scooter, that is totally house broken, he goes outside on his own (doggy doors). When we are all outside, Scooter will mark each & every pee or poo done by the other four, even if it's just a drop. He considers himself to be the leader of the pack, after me of course becuase I control the food!
