Oh there is. If you do power restoration missions you can go around after powering up the base and check the data ports. No enemies.
As for the on-foot fighting, if I can do it anyone can do it. I'm terrible at FPS type games.
I'm also 72 and slow. I wasn't fast when I was young and haven't improved!
But Odyssey is more about being smart than being fast. I have practiced, and I'm stealthy. I can take out an entire base full of people if I actually need to, and never be seen. But most of the time I don't have to fight at all.
The actual fighting is a bit like RPG stuff, similar in my mind to Skyrim or Fallout. It's not super demanding.