I don't think you have to give up on running, if it's what you want to do. I know many runners that did not start until in their 50's and they are still going strong in their 60's and 70's.

Some other people have already mentioned that form is very important to prevent injury and I would strongly second that. I've coached some "grand masters" and I will have them do a drill workout twice a week. Then a longer workout following one of the drill workouts. I have them do all their drills on grass. As for speed, if you want to do speed work, do it in the pool using an aquajogger and do high intensity intervals of 2 to 3 minutes with 2 minutes rest after about 5 to 10 min warm-up. This is great for training fast turn over and muscle strength while not stressing the joints.

I know of a lady that was a nurse and at the age of 55 she tried to run for the bus one day and was so out of breath, she was mortified. She could not believe her lack of fitness. She started running by counting lamp posts. Each day she would try to add one or two to her very short runs. This same lady did her first marathon at age 63.