Well this is the hard part. You have to let him know you are the boss (you are, aren't you?

) When he starts bouncing around let him know that is not acceptable when he is on the lead. Make him settle down and pay attention. The first step is for him to just stand without fussing. Keep his attention focused on YOU -- not on his stablemates.
At first don't be too fussy about him not standing right next to you, just get him to settle and pay attention to you. Use the rope over the nose to keep his attention on you. Remember, to keep the lessons short and take
tiny baby steps.
1st baby step, have him away from his buds, paying attention to you and standing still. If you can hold his attention for a 30 seconds to a minute you are starting out well. When I said baby steps, I meant it! Make sure you give him rubs and scratches as praise, but don't let him get at all nippy with you. As long as he is on the lead line, you are the boss not his playmate!
Remember to work in short bursts, his attention span is very short right now. But do this a few times a day if you can. I know when you are boarding, it's not easy to be there every day. Be consistant, but if something isn't working, don't be afraid to try a different approach. If you find you are getting angry (and don't worry, it will happen!). Put him away, go throw a temper tantrum (well, it works for me) and then come back to him when you are calm.
Don't be afraid to correct misbehavior. Nipping, for example is something a colt his age is bound to do. A good solid bop on the nose is in order... but never EVER hit him when you are angry. When you are training, you have to be in control of the horse AND yourself.
I was young when I had my first foal to train, so I know some of the issues that come up when you are younger. To some folks here that are older, they might not understand the cautions I am giving you.
But the most important thing to do is just go ahead and start working with him. Being afraid you will do something wrong will only cripple you and further delay his training. You will make mistakes. Even the most experienced trainers do! So don't freeze up with fear -- just get out and start working with your little guy.
This is an exciting time for both of you, don't forget to enjoy it!