When I was a child, I ran everyday. I ran up hills, on streets and in fields. I didn't have to train to run, I didn't have to think about it. It was just a natural thing to me. Many of you probably had the same experience growing up. Running after 50 isn't so natural. You have to work at it until it becomes easy for you.
Start running g-r-a-d-u-a-l-l-y. Don't sabotage your efforts by trying to do too much too soon. You may be able to run only a few minutes at the beginning. That's ok, you started. Keep at it. Don't give up! The rewards are worth the effort. Endurance will come. Now Get Out there and Try It!