HHMMMMMM, well, I'd say too, it's mostly just his age:). I guess I'd start first with working on making him stand still. But that isn't something I teach with treats.
Have you ever watched any of the Clinton Anderson shows? On things like that he would just make the horse start to lunge. IOW, when you ask the horse to whoa, if he doesn't, or doesn't stand till you ask him to move he immediatly starts them lunging, and not just a time or two around. Eventually the horse figures out, it's easier to pay attention.
Anderson does that for about any problem, loading, pawing...It takes some commitment:), and can take awhile, so don't start unless you have a lot of time. I also wouldn't ask him to stand for long periods of time at the start. Kind of get a feel for how long he will stand before moving on his own, and only ask for a tiny bit longer. When he does it satisfactorily either let him go, or work on something else. Then come back to that later.
Becky
We have been having attention problems when lunging too and when he did not pay attention I made him go more. That did seem to help, but as you said you need a lot of time to do that of which I have little. I do lunge him when I can. I do not have a round pen so have to go down to the neighbors to use theirs. It gives him time away from his buddies which he hates and has a hard time concentrating at first but eventually settles and catches on.