Try biking instead. Similar to running, it’s an individual exertion you can do outdoors in the fresh air, but smoother and lower impact on the bones and joints. No shin splints or other impact injuries. You can often find a used but quality brand bike on Craigslist for ~$100, which is sufficient for just exercise.

I actually switched to a treadmill and took a course in running and minimalist shoes (which I thought were BS before) and changed my running form. Got rid of my shin splints and knee pain. No impact issues... was a weird transition, though. Learning to run like a boxer stands was more difficult than I thought it would be. I can run for about a mile, mile and a half on the concrete, outside before I realize I'm doing damage and have to stop... getting old sucks =) I do have a bike, but somehow it doesn't do the same disassociation for me. Not sure why. I think it has to be something I hate, personally, to get me over the hump and force me out of my own body.

Or kick bikes. https://en.wikipedia.org/wiki/Kickbike