Augie was around 17 months when he was altered. He went through a humping phase when he was younger; if we were sitting on the couch with our legs up on the couch, he would try to hump our legs. We just discouraged his behavior. He wasn't a roamer - I guess we don't give our guys the opportunity to roam. They are always accompanied by us when they are outside. Finn is approaching two and he is still intact. I took him in at 14 months, and the vet clinic was extremely busy on his scheduled day, and they could not assure me that he would get to come home the same day, so I wouldn't leave him for the procedure. It was shortly after that, that we noticed he was having allergy issues with a lot of ear infections, etc. and our vet didn't want to put his body through more stress until we had that under better control.
I would suggest that you do your research so that you are aware of the pros and cons. There are differing opinions on this. From articles I read, I just knew that I wanted to wait until at least 14 months or so for the benefit that the hormones provide for bone growth, etc.
I will say that Finn has been a humper from the get-go - but I have only seen him hump Augie - and he also started marking in the house. He still does not have free reign of the house, although I haven't seen him to try to mark anything for several months now. If I can't watch him, he is gated in the kitchen or crated. He had been trained for quite some time on a UgoDog, but when the marking started, I decided it was time to get him trained to outside. I think he has gotten the idea that outside is where you do that.
Linda, Augie & Finn's Mom