I'm guessing maybe, but for some people, getting an ache after 6 miles might be 'normal'? That is of course assuming no actual foot damage or malformed bones, feet etc. I often go through periods of one sort of ache or other, usually during the first two or three days of a hike, sometimes I decide to walk through it, sometimes I stop and rest, massage my feet and so on. I have even found that, for me, it is worth stopping there and then for the night (or not going much further) I lay horizontal, on the odd occasion I could be on my mattress for about 12 hours, I wiggle and stretch my toes and feet and by the morning my feet are back to normal or near normal. I also always wear inserts, in my case Sorbothanes, they help my feet comfort a lot.
Some people I know get shin splints even while walking. I used to get them by running, just can't rember how I solved the problem. I think is was a combination of massaging, rest and walk, run, walk, run?
I have walked for a number of years now and I've never noticed that my feet have hardened up, my skin is supple and they just stay that way. In fact I have come to believe that supple skin is imprtant, it allows flexibility with in the boot.
I would suggest you need to understand 'you', to try to understand why you feel like you do, what sort of feet you have, your gait and so on. I hope some of this is of help.