That's it, you see. I don't see the older snake fighting at all. He doesn't raise his head. He rubs on the smaller snake and gently will nudge him here and there. He doesn't try to grab a hold of him to constrict or bite. Not even when he was bitten by the small snake did he try to fight (and he is the bigger snake). The smaller snake doesn't like it. That is pretty obvious. The little snake is aggressively trying to stop the behavior but while they were together, he couldn't get away from it.
Looking at several mating vids, and even an alleged male on male mating vid still makes me think its sex for the old guy, not territorial. Again, why is this snake being territorial only to the small snake while the 3rd male snake in the cage is left alone? Why still restless in that cage after the little snake is removed? Yet no efforts to move against the 3rd male snake. I've read that larger snakes can attempt to mate with smaller male snakes and, in the wild, a smaller male snake may allow it for self preservation.
Anyway, trying to figure out snake psychology. I just find this extremely odd that its starting now after 16 yrs. And no, I didn't miss this behavior for 16 yrs. I'm pretty observant and take care of my snakes.