He's growing nicely and looking good.
To answer your question feeding in the cage as well as feeding live food can make them territorial, food aggressive and or increase their feeding response. To where they will want to go after things that move like fingers, toes, graduating to hands and or feet as they get bigger. I could be wrong but that doesn't look like an FT pinkie to me.
With the tail whipping being a poss set up issue,.. they can try lowering their hand into the tank on the opposite side from him and approaching slowly at his level. To see how he reacts and or letting him come to them before trying to pick him up. Also when they go to pick him up use the palms up method instead of over hand. Since your hand over them mimics that of a predators claws or mouth. Which will trigger one or the other of the fight or flight response.
One thing I noticed just from looking at the pics is the tank is dry and tegus require humidity to aid in shedding just like Bps. Not enough humidity and they have retained pieces of shed that can cut off circulation to their toes and tail. If they drop or lose a part of their tail it will regenerate (not the same pattern or color) but their toes will not.
They grow fast when they don't hibernate and his body length is already longer than that tank is wide. I give it another 2mths no more than 3 and he'll have difficulty just turning around in there.
Thetegu.com and tegutalk.com are 2 great sites they should check out for info.![]()