You can do it!

I have a lousy knee, have since I was a kid (I"m 48 now). The key for me is good, cushioned shoes, with cushy insoles. As soon as your knee starts to hurt, replace them. It's worth the money.

One thought on training: Start with a run/walk plan. Run 2 minutes, walk a set amount, 1-5 minutes, then run 2 and walk, etc. Slowly, over weeks, increase your run/walk ratio. You'll be surprised how you can pick up the mileage. It also gives you a good idea of what your knee can take.