I wouldn't worry about it. I read some people want to restrict the distance of walks but I'm a strong beleiver that the dog will tell you when he had enough or tired. It's not a bad thing to stop a few times along the way and let him smell the grass, lay low and enjoy the breeze a little bit. If he whines a bit and you have to pull him from behind you, then... if you can... just pick him up and walk home for him to rest in your harms.
I can't see the damage it could cause as if he's no walking he could be at a daycare playing with other dogs for about 7-8 hours straight. If he'd be raised on a barn he'd probably be outiside all day long discovering his environment and respecting the long heritage of Corgis.. :)
Yes he's still a baby and as any children they will tell you when they have enough. Good idea on the hikes cause my Wally just goes like a rocket in the trails, groomed or not. He tends to slow down on sidewalks and where busy roads are, he doesn't seem to know where to go or being skiddish a bit. It's a good practice to get him sensitized to this but when we're isolated in the woods a bit, with the smells and wildlife, he's in his elements.
I brought Wally for a 7.5km (4.6 miles) when he was about 9-10 months of age. It took us about 3 hours but he surprised me the whole way. We stopped a few times to get some air, lay in cool and crisp stream waters and enjoy a waterfall. We'll go back for sure this summer once it dries up but for a little pup he was like a SUV, keeping at the end of the leash, over boulders, tree roots, fallen branches, etc.
Just be attentive of his body language and if he gets anything in his paws or seems in distress. Enjoy the outdoors.
Two miles is fine. At 7 month he should walk enthusiastically and be able to outwalk you on natural terrain. Temperature is more of an issue, especially heat. Even walking on pavement would not be a problem. Jogging, running alongside a bike and such are a different issue.
Like someone else stated, the dog will tell you. I've walked long distances like so with Gible and he absolutely loves it, he keeps going and going. When he was a tad younger, we would have to stop to let him rest and keep going, but ultimately if he was super pooped we'd pick him up he was completely content and relaxed. other times he wants back down so he can continue to walk. that tells me if hes had enough or not haha.
I wouldn't worry about the amount of exercise you are doing, I think you could actually do more if you wanted. I walk my 6 1/2 month old Cardi Lucy most days for a 1.5 mile loop around the neighborhood (35-40 minutes total). Usually, she still has energy left when we get back and would probably walk farther if I'd take her. I take the walks at Lucy's pace, walk as fast/slow as she wants to go. I sort of consider her my "personal trainer" because she adds variety to the walk. I've started wearing tennis shoes because sometimes she wants to do little spurts of running, so I'll run with her. Then she stops to smell something and we rest, then start walking again. I try to keep her walking moderate since she is still developing. Occasionally, she gets tired during this walk and I'll carry her for a block or so, then let her walk some more. Lucy usually stops, sits, and looks up at me when she needs a break. I agree with everyone else, as long as it isn't super intense activity (running/jogging for extended periods of time) your pup will let you know when he's had enough. Have fun! Walking with Lucy is something I look forward to so much because it's so fun to see what she gets intrigued by :)