What is the truth regarding running and joint pain ?

Maybe it has something to do with what you're running with or running on. Running on concrete or asphalt outside with poor cushioning like many shoes lack can cause some joint pain even among seasoned young high school cross country runners. Running on a cushioned treadmill or with good shoes outside can help prevent the joint pain. The studies go both ways on running either strengthening or hurting the joints. Either way I don't think you should give up running, it has too many benefits that outweigh the risks imo.

Several studies have shown that there is no connection between running and arthritis. Researchers at Stanford University conducted a study on 1,000 runners and non-runners for 21 years. Their data found that runners' knees were no better or worse than non-runners' knees.

My great grandfather is over 100 years old and he runs 10 miles a day, 365 days a year.

The truth is that it varies, because some people are predisposed to joint issues, arthritis, etc. Bottom line is running itself doesn't cause joint pain if the person has good form, BUT if the person has poor form or pre-existing issues or genetic conditions that predispose them to joint issues, then running can exacerbate those problems. 

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Some ways to help reduce the chances of running injuries are:

Wear quality running shoes suited to your feet and biomechanics, and change them out every 350-500 miles (depending on your running conditions, style, and weight)

Warm-up and cool-down/stretch before/after your runs

Foam roll and do self myofascial release regularly (with a tennis ball or similar)

Strength train to help your body stay strong and better able to handle the high impact pounding of running

Talk to a good running coach or physical therapist skilled in running technique, to ensure your form is not one that will lead to possible injury (some physical therapy clinics or personal training facilities can do a gait analysis and help you see if there are any issues or potential issues)

There's no way to tell how it will affect you, as an individual, except to keep running until you are 50, or 60, or 70, or ...

Some injuries that affect running are the result of non-running activities. Even so, a lot of runners have injuries caused from running. These tend to be repetitive use injuries, with causes that are correctable.

I believe running injuries can be prevented by avoiding mistakes. 

A common mistake is running in shoe that poorly match the runner's biomechanics.

If you feel some pain, find out what is wrong. Find the cause, and correct it early.

I'm a fan of othoses (orthotics). These can compensate for biomechanic issues not corrected for shoes. There is a good chance there is something different on your left than on your right, so an orthosis can be used to balance your left and your right.

Personal note: I've had mild knee pain starting when I was a kid. It doesn't bother me when I run regularly. I believe running is good for my knees. I have had knee pain, but I dealt with it by modifying an insole one one shoe. Essentially, I made my own orthosis. 

It is possible your mother has joint aches because she *didn't* exercise regularly. 

Of course, there are many other possible reasons for your mother's aches in joints. She should go in for a medical evaluation. She should ask her physician about her risks from an exercise program. 

The truth is that some people have no issues over the long term, and others have issues. Do your parents, grand parents, have joint issues?  If yes, then most likely you will too but not all the time. If your grandparents and parents don't have any issue, you probably won't either.  Other things come into play like injuries, diet, over all health and such.  Injuries that you have when young, come back and haunt one when old.  Especially minor fractures that one may not even have known they had. They suck to be honest. 

How active has you mom been during her life. On her feet moving most of the day or sitting around eating bon bons?  Makes a difference. Can't go by weight though, too many judge on that. If one has been active, then has health issues, it is very very difficult to adjust to a less active life style. Everything has to change from how much and what one eats, to mental health becouse suddenly being limited takes a toll.