I did the biting of the nails and the chewing of the cuticles from childhood well into my 20s. At some point about 10 years ago, I made the conscious decision to stop and quit cold-turkey. Haven't done it since, save for the odd piece of nail that sticks out on occasion.
My cuticles are still horribly scarred and mangled and will never heal. Even 10 years later, it looks like I still do it.