I have a few that don't particulaly like their tails touched. Does he so that when you touch him on the body or neck? If he is OK with other parts of his body and doesn't jerk, I would think it just makes him nervous to have his tail touched. Remember, they have instict to flee from predators grabbing at them as a meal. I may just be his natural response. Baby snakes are a food source for many predators in their natural habitats.
As the others above me have said, too, babies are also more nervous. He'll probably grow out of it. When I handle a baby I do very little touching at first. I just let it get used to being held on my hand and let him get used to it on his terms. After several sessions I start to pet it after it looks like he's comfortable and relaxed on my hand. I think instilling trust with the baby with as little interaction as possible is important.
If he's eating and pooping and all, I wouldn't worry too much, but if you are concerned take him to a vet. He may also be constipated or have an injury that is tender???
Best wishes with him!
-----
Cheers,
Jessica Gibbs
Ball Pythons; Corn Snakes; Green Tree Python; Jungle Carpet Pythons; Bci; Bcl
3.0 Crazy Dogs and 2.0 cats
Some Tropical Fish
...........and growing!