Everybody ages differently, so it is difficult to tell what would work for you. You need to try and listen carefully to how your body reacts. I agree with the posters that suggest cross training and I would add also that it is very important to work on core and stability to save your joints.
In my case, I used to be a low-volume/high-intensity guy that would get injured every time I would run more than 50 miles/week; but I could run three hard workouts in a week and race on the weekends.
Now, I can manage only one speed workout every second week, but I found out that, without the hard workouts, I can manage 60/70 miles per week without getting injured, so my training is based on a lot hilly miles with some fartlek and thresholds.