I had similar symptoms, and took October, November and December completely off -- no running, no cross-training -- and had ZERO improvement. This was after marathon training through the pain for five months.
In January, I joined a gym and worked the Nautilus leg machines a few times a week, and got on the elliptical trainers for 40 minutes while at the gym.
After only a few weeks, I was able to gradually introduce running and have built up to about 45 miles a week. I have recently added VO2max and threshold workouts. And still do the Nautilus machines a couple times a week, but plan to mostly switch to lunges, squats, leg lifts, etc.
The knee discomfort is still there, but it's manageable. It doesn't wake me at night anymore, and I can sit for prolonged periods (like at a restaurant), without the throbbing pain I had previously. Walking down stairs is still uncomfortable, but much improved.
I am assuming it is "runners knee," and addressing strength imbalances is helping the patella to track properly with less irritation.
I am 58, so even older than you. Marathon pace last fall was 7:08/mile, so definitely not a speedster, but still running reasonably well, and getting back to those paces as the fitness is returning.