There's a lot of runners who say that weight training should be low reps, heavy weight. This builds explosive strength and not size. This has been backed up by Alberto Salazar. However, looking at Haile Gebreselassie and Kenenisa Bekele who I knew did high rep, low weight work and you can tell as their form rarely dropped especially Bekele during cross country. Then there is the Kenyan's who seem to do barely any weight work and just run lots of hills. What is your opinion on strength training?
If you're weak or have imbalances then you need to strength train. Most people have weaknesses and imbalances because of overusing the same muscles everyday or because of an inactive sedentary lifestyle. Runners who have desk jobs and sit 8 hours a day probably have some form of dysfunction.
Figure out where you're weak and strengthen those muscles, figure out where you're too tight and mobilize those areas.
Aging runners should strength train to optimize health and fitness. According to Dan John certain areas such as the lower traps, rhomboids, triceps and deltoids tend to weaken and muscles such as the pecs and biceps tend to get tight as you age.
I do a lot of leg workouts. Ab and back workouts. Doo 1 to 2 day's a week of upper strength workouts as well. I do a little crazy workout. Do 2 days of not heavy reps. Instead increased reps and increased speed less rest. Plus do kettleball and stretch prior to working out. Plus I do plyometrics during workouts and through the week as well.
Also do hills, interval training, and sprint workouts through the week. Do a lot of low mileage runs, but a lot of mileage is done during one run a week. Try to have 2 rest days a week.
Probably do about 4 to 5 hours a week of lifting.