well... i'm glad to find this post! one of my boys, duncan, recently started to bite the tip of my fingers, mostly the nails. i don't have long nails, mind you, so he's biting the wider part of my nail. he never bites hard, but since he is the only one that does it out of my three boys (all brothers) - i began to wonder if it had anything to do with boys and aggression. it seems though, drawing from the other people who have posted, that it has nothing to do with gender... so i'm hoping its truly has nothing to do with males, age and aggression.
as for licking... all three of my boys lick - whether my hands are just sweaty, from a day out at work, or just out of the shower - it does not matter, they lick. cowboy, most especially likes to groom me - he's teeth will rapidly nibble over my skin, almost like eating a corn cob. I don't think this has anything to do with salt - and more being loved and treated like one of the pack. they groom me, like they groom each other. black jack looooves to groom my scalp, which is hilarious and it makes me feel like a gigantic rat.
when i first got my boys i had bought them a salt wheel, which went ignored for months before i decided to take it out of the cage.