I'm running 2.5 miles twice a day. I know that sounds absolutely silly but I feel like it's a good plan. Im 32 and I've been running since july. By the beginning of October, I was at about 45 mpw and became injured with itbs/patella tendonitis. I've been working with a good running chiropractor and he said i have weak glutes/hips and inflexible ankles. He has me doing PT and I seem to be nearly healed. He told me to run when I feel good and not to run when it hurts. So, I'd run for 2 or 3 days at 4 or 5 miles and my knee would be sore for a few dayd and then I'd repeat that cycle. I decided to split that 5 miles and run twice a day and see if that got me through the week without pain. So far so good. My goal is to eventually get to 60-70mpw and I feel like getting in to a doubles routine will help me get there much safer.