I'm a former runner too. I ran from 1981 to 2006 (Aug.) Subtract some time off for having my two boys
I'm now walking everyday, usually a three mile hilly course. My best time so far is a 13 minute mile. I have found this to be really enjoyable and my muscles still seem to be very toned.
I also have a Soloflex that I use 3x a week, and a Total Gym that I use 3s a week.
My husband and I are also learning to do Pilates.
I miss the fun of being able to run, but I'm doing my best to make the most of what I'm doing now.