15years ago I was showing visitors round where I used to work and one asked me if I was okay as I was limping. I'd walked 20miles the day before in the Peak and my knees hurt. I've been for an hour's walk this afternoon and my knees still hurt! Life goes on I find my knees are worse if I rest for a day or two. Why don't you try a few 3 or 4mile trail runs? Keep off the road, and don't go mad but just see what happens