So there's this thing that foals do, it's called snapping. My 20 year old gelding still continues to do it many years later. Feeding time, and occasionally during rides. Any thoughts on why he does this?

Some horses will continue to do it if they are especially subordinate in the group. Foals do it to show that they're young and not a threat - an older horse is doing it to show they are not a threat as well