I really wanted to quit. I put a rubber band around my wrist and any time I found my fingers heading toward my mouth, I had to snap the rubber band (hard ) five times against my wrist. Took about two weeks, but I stopped twenty years ago.
I quit last year. I said once I turned 21 and was a "real" adult, I had to stop. What worked for me was buying the polish that tastes terrible. It's by OPI, and I think it's called No-Bite. It's clear, but it tastes awful - between that and a determination to quit, I was able to stop.
I'm not an adult, but I have bitten my nails my entire life. One thing that really helped me was carrying a nail file around.. my nails are really weak, and when one would start to crack or peel, that's when I'd start biting it. With the nail file I could just file it down and it wouldn't bother me as much. Keeping my nails painted worked for me as well. imo, if you are really determined to quit, you can. Start to notice what triggers it.. another thing for me was sitting in class bored out of my mind. I'd start peeling my nails off out of boredom - but now that I'm not in school anymore it's not as huge of a problem. Good luck