How can I stop biting my nails?

So I've got this habit of biting my nails, I've been doing it since I was 6 Now I'm 14, I really want to stop because it's sort of interfering with my life, I also bite the skin and It bleeds alot. My hands are covered in peeled skin and the layer on top of my nails are damaged. I can't help it, I'm a guy so I can't wear coloured nail varnish or fake nails.