@Discombobulated
It's awesome that you started running in your 40s and inspiring that you ran half marathons then too. I am the same with not being able to do sprinting or even fast running times but I can work up to longer distances. In my 30s, I got to the point where I could have run half marathons but stopped a lot of the jogging after I had a fall running and ended up with microfractures in my hips. That is an injury I wouldn't wish on anybody. I had a ton of pain, and the fractures didn't show up on initial imaging so while I was begging for painkillers, all the providers kept thinking I was drug-seeking and wouldn't prescribe me anything for pain. Several months later, my rheumatologist believed me and sent me for another X-ray; this time the microfractures showed up vividly. I was sent for MRIs and finally believed and prescribed painkillers at the point at which I was finally starting to heal and hurting much less. That made me shy off running for a long time, so I started walking instead.

Then, I developed bad peripheral neuropathy in my feet, and I had to stop even walking for exercise and switched to pilates. But then this May, I was put back on Cymbalta, and the tingling associated with the peripheral neuropathy went away completely within a month and later I was put back on lamotrogine and the cramping in my feet associated with the PN went away, and I started walking again for exercise and then decided to start the 10K runner program which I'd used in the past. I still have numbness in my feet associated with the PN, but I can live with the numbness; the numbness is much less bothersome than the tingling & cramping were. And the numbness is not that severe.

I do feel proud that I have worked up from having difficulty with 1 min intervals to being able to run 10 min. intervals even if it is a challenge for me right now. I definitely feel my fitness has improved quite a lot doing this program.