|75 years old and FAST!|
When someone; even a doctor tells you that running is bad for your knees, hips, etc. You can refer them to any one of a number of fact based studies that have been actually done on this subject.
For example, one is referenced here in an NPR article:
And another study by Standord University:
And then there's this one: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2556152/
There have been other studies as well and more continue to come to light that show the benefits of running not only outweigh the downside of running, but that the downsides of running have been FAR overstated to a point of being folklore instead of rooted in any basis of facts or actual data.
Many people (including doctors) operate under a false set of myths, perpetuated in spite of these such data. Many doctors themselves, don't live healthy lifestyles - nor are they qualified in areas of sport's medicine or holistic preventive care. (For example: I recently told a doctor I knew that I was slightly sick because over the past couple of days, I felt a decreased aerobic function when running up a flight of stairs or pushing hard in my workouts. He told me I had life-long asthma and wanted to prescribe an inhaler. I'm currently looking for another doctor.
The FACT is that long time runners (that have done it 'right') have FAR lower rates of 'lifestyle' type health issues (heart disease, obesity, diabetes, cancer, etc.), higher bone mass and muscle mass retention with aging, AND actually have been shown to have LESS degenerative issues with connective and cushioning tissue than sedentary people.