Holly,
The quickest way for me to want to prove to someone I can do something is when someone tells me I CAN'T.
Let me explain.
Two years ago I was scheduled to have 2 knee surgeries. The reason was because I was extremely overweight and I loved to walk. Just like you. I was told I couldn't walk anymore because I'd completely abused my knees to the point of causing arthritis, to try other things... and I myself was only about 36 years old.
So here's what I did instead.
1. I cancelled my knee surgeries.
2. I scheduled myself to have my Lap Band removed and replace it with a VSG.
3. I let myself recover slowly but surely.
4. I did other workouts to help me continue to lose more weight.
5. Once I got to a certain weight, I started walking again.
6. I continued to lose, and I continued to walk.
7. I signed up for my first 5K running event.
8. I ran that 5K, from start to finish.
Today I have ZERO knee pain, and I didn't even ever need to reschedule my knee surgeries.
Do NOT lose hope in that you will never run a 5k, 10k, Half Marathon, or a Marathon. NEVER IS NOT IN YOUR VOCABULARY.
Now, dust yourself off and keep doing what I know you can do, and that is keep working to be a better, more fit and healthy you.