I dont bother with mileage nowadays,I do two or three 45min to 1 hour runs and a hour and a half on a Sunday. All off road if possible. If you avoid tarmac and concrete your knees will thank you for it.
My advice for anyone just starting to run, would be ; dont run more than three days a week. Never run two days in a row and try to run offroad as much as possible, also listen to your body, if you have pain.Rest,its just as important as running. Best of luck