I am a 51 year old male and have been picking my nails for as long as I can remember: I even held my school pencil in a different way to hide my nail. Even then I was ashamed.
I absolutely dread some social gatherings, especially meals, where the person opposite will have a front row view of my horrible fingers. The more it frustrates, the more I picked.
Clenching my fists in public, elastoplasts on fingers I've done it all:'(
Anyway, around five weeks ago I noticed I hadn't been picking for a few days. This was strange as I rarely managed a few days without. When it reached eight days with no urge, I started to look at any significant changes in my lifestyle.
On returning from holiday, I'd felt a little run down and sad, I started taking vitamin tablets that I'd bought in local supermarket. I bought multi vitamins, vitamin B and vitamin D and was taking one or two every morning.
This was the only thing that had changed in my diet/ lifestyle and as a matter of curiosity, I googled "vitamin nail biting" and actually found several articles on this matter, which ultimately brought me here.
I am not saying this is some kind of miracle cure, but for the best part of five weeks my nails have grown considerably. I still have the odd, impulsive relapse but have managed to contain it to my thumb, that was minimul though.

Keeping in mind, my left hand especially, nails were down to around 1/8 of an inch, they are looking much better. I'm hoping in around another four weeks that I can finally lay my hands on a table and relax.

I have been suffering with this for so long and my heart truly goes out to anyone in this position:-) it may be worth trying the vitamin route, I mean even if it doesn't work for you, you get some decent vitamins inside you:-)
Good luck guys x
David