What can I do to stop my horse from being so pushy?

So my green 5 year old is a pretty good trail horse. With only 30 days on him, he goes on 1 hour rides and usually does fantastic---except for a few things. So Eros is awful about staying away from the other horses' s. In fact, he goes right up to them and will start rubbing his head on them! Thankfully, I've been able to keep him behind calm, nonkicking horses, but I really don't want to have to constantly worry about whether or not the horse kicks. I try very hard to keep him off the other horses, but usually at some point he'll just start mostly ignoring me. He's the worst on downhills. He's extra pushy (not like wanting to gallop, but like wanting to invade the other horse's space) and difficult to control. I know I this is all normal for green horsesand, as far as acting up goes, this is pretty mild (and the absolute worst he does) to do at first, but this behavior drives me crazy. It gets me sooooo frustrated sometimes! What should I do?