Hi Linda,
I am 54, new to running, and with flat feet as well. I'm so excited to finally have the ability to fulfill my lifelong dream of running further than across the street without causing severe pain in my feet and ankles, likening it to mini-sprains. This pain used to cause me to nearly fall every time I attempted to take off on a run, and I would limp away till the pain subsided. Walking was also very painful for me, even after trying every type of over-the-counter insert, and many different shoe types.
I feel I am able to run only after getting custom made orthotics from my podiatrist. I told him about all of my lower extremity problems since childhood, and of my dream to be a runner. It took about 4-5 months of getting my feet, ankles, legs and knees used to my new orthotics, but everything is finally in the correct alignment. I am only starting week 2, but I am ecstatic that I am actually running, with zero foot or ankle pain!
I am feeling good and confident that I will succeed because - I CAN run!! Check with a reputable podiatrist, and invest in some custom orthotics, they just might work for you like they have for me. Good luck to you in reaching your goal.