Typical behavior from a colt, or even a young filly...just keep doing groundwork with him, especially concerning him staying out of your space...if he is not in your personal bubble, he can't nip you...if his feet are moving he can't nip, and will have a harder time rearing, etc...
I would be working on getting him to do "more" in regard to moving his feet; start doing hip and shoulder yielding, backing, sending him both directions (think over objects, or between you and a fence, not in a circle), you can even teach him side passing, using a fenceline...different stuff that will keep him moving his feet, and using his brain constructively
When he was born, I missed the birth itself, but did many of the imprinting exercises with him, so I had him moving off of finger pressure and backing up, moving sideways, etc. right from the get-go. But I didn't do anything to make him respect my space.
So now my friend who helps me with him has me backing him away from me, disengaging the hindquarters, *trying* to lead him calmly from both sides, elbow him when he puts his head in my space or tries to nip when leading, etc. So I am trying to do some things like that.
But with my first training exercises I was just using my fingers to press him to get him to move over (and he actually does a decent sidepass and backs up that way) but now I am using a dressage whip to teach him to back up, keep up at my shoulder, etc. and trying to make him get out of my space without me actually having to touch him. So I kind of switched to a different method that the one I started with, and one I am not that familiar with myself. I also use a "kiss" as a cue that I want him to move his feet, and now when I kiss (like if he is lagging and I want him to step forward more) he actually pins his ears. It's like he does it, but he hates it, and the kiss is a cue for him to get mad at me.
So I don't know. I want to keep things positive for him, but I kind of don't know how. I want to quit on a good note, but when he's acting obnoxious I don't want to stop until he does good. But then the sessions end up taking longer than they should. It's kind of like "please be good so we can quit before things get worse." I start out thinking positive when I work with him, then get very discouraged by the end of the lesson. I don't want to burn him out, but I don't want him to walk all over me either. I don't want him doing these things when he is 1000 lbs.
I really hope gelding him helps. Or maybe at some point his mind will mature.