I have a ~5 week old male kitten. I've been raising him well and he gets a lot of attention. He purrs every time someone touches him and is a generally happy kitten. However, I am wondering if I should be allowing him biting my fingers. He enjoys a 'game' where he lays on his back and I tickle his stomach and he tries to grab my fingers (with his claws extended) and if he succeeds he ends up biting them. He is definitely aware that this could potentially hurt, as he never extends his claws nor bites my face, even when touching it, but he does do so with my fingers. It doesn't really hurt since his teeth are only just growing in, but should I be stopping him from doing this? Will this lead to a bad habit, and leading him to potentially painfully bite people/me when he is older and has stronger teeth? If so, how do I show him this is not ok?
It's generally not a good idea to encourage cats to play with your hands. Some few cats are gentle enough that this can be done without your getting scratched or bitten, but most cats aren't that good about it. As a kitten it might not hurt you, but if the behavior keeps up into adulthood, it probably will. It's really difficult to teach a cat how rough is too rough, so it's probably better to just exclusively play with toys. The cat might still attempt to play with you rather than its toys, in which case you should attempt to redirect it by drawing its attention to a toy instead. For instance, waving a feather wand at it, or tossing one of its toys towards it.