Lollo did that from about 12 weeks until he was neutered not too long after! it’s a lurve thing, the biting / nipping is part of the action and human legs do seem to do it for male bunnies! I would definitely get him neutered and the sooner the better – you don’t want him ‘learning’ other bad habits that are driven by hormones that will be difficult for him to unlearn.
and don’t worry too much either, if you find a good rabbit-experienced vet to fix him you should see an improvement in no time. Lollo was precocious and his urm ‘balls’ (more like almonds!) dropped at around 11 weeks. some vets i spoke to wouldnt even entertain the idea of neutering until he was 6 months. however the vet i found and use now (it has an animal hospital attached so they do a lot of surgeries) said in her experience as long as the bits were all there and the bunny is otherwise in good health there is no reason to wait if the hormones are causing problems.