HAHAHA! its so interesting you bring this up. im 21, and I just stopped!!! I know its v hard, but what I had to do is I bought that clear polish that tastes bad when you bit your nails. i brought it everywhere with me, (cause washing your hands and such makes it come off) so that i would never be tempted. then i would do small things like painting my nails (only for girls, unless guys like that sortof thing!) and making them look nice so that i WOULD WANT to grow them longer. i just got to a point where i said it looks gross, and i have to stop!!! plus, the biggest help was telling people that i wanted to stop so that if i started to bite (you do bite without realizing it!), people would yell at me and say that its nasty. so i would say people telling me that i should stop really made me want to kick that nasty habit. plus, im proud of myself. believe it or not, but it was hard (as funny as this sounds) the only set back i found, was that when ever i got nervous i would always bite my nails. but because i stopped, i had to find a different way to release being nervous!!!!!!!! oh well, the feeling after you've done is good,,,something to be proud of,,,,good luck