I used to be a keen runner in the past. When I was forty, I could do a half marathon in 1 hour 18 minutes. It is important for those who have not been running recently, that they start SLOWLY and GENTLY and do SHORT distances, gradually increasing in all three dimensions.
If you don't start easy and build up, but instead just rush into it, you will suffer for it and this will stop you continuing.
A good approach for the non runner wanting to get fit, is to walk 100 paces, or a fifty meter lamp post interval, then slow jog the next same interval, and then walk, and then slow jog. After a daily round of about a mile like this, after about a week, increase the speed a little, and do another week. Then double the length of the running distance, but keep the walking one the same. Then stop the walking and run the mile for a daily exercise for a week or two, then do two miles. Pretty soon you will be doing half marathons if you build it up like this.
No pain
No exhaustion
No bad joints.
People who have heart problems should talk to the doctor first. Other people can just do what I said above. Never keep going as a beginner if you start to feel bad. Just walk home and sit down.