This is actually surprisingly common in cats of all ages, and as you’ve probably guessed it is actually a sign of affection. Most cats that indulge in this behavior gently bite and tug clothing or hair, as apposed to the actual skin. While it’s understandable that you’d want to discourage this behavior, you also do not want to scold your cat when doing this because he may feel rejected. Therefore, the key is to make it unappealing, for example by applying Bitter Apple to a small area of the skin where he is likely to bite. 

It is possible that what your cat is doing constitutes suckling behavior, which is thought to occur in cats that were deprived of their mother at too young an age. This can be approached in the same way as gentle biting – see the resource link below for more information.