I hear you there, since becoming disabled the whole direction of everything in my life changed. Finding new things to keep myself occupied has become a necessity. Finding that sense of structure in walking is a good idea. It's not the same as being a Marine, but it gives you something to work at. I know some days I struggle to get anything done. Retirement does take a huge chunk of your life away, but it's good you're finding things to slowly fill the void is a great thing!
Same here with regard to the medical retirement. I am also thinking about starting up a part time virtual consulting business, but I don't know yet. I did it once and it didn't work out so well. Then again I tried during my dark days when I lsot my mind for a while. So maybe now, with a level head, I can manage better, especially being just a part time thing.