On our last trip we were in the parks for six days with our (then) 8 and 5 year olds. We did not use a stroller. I was a little concerned beforehand about my 5 year old begging to be carried at certain points, but we found there was so much to stop and see, and rides, shows, and meals to break up all of the walking that the only time we encountered a need to carry her was one evening after we watched IllumiNations in Epcot from the back of WS. We did take a mid-day break for swimming each day, so that helped re-energize the kids. The temps were also in the mid-high 80s with moderate humidity. If we had gone in the summer at peak heat and humidity, we may have had to get a single stroller for our younger daughter. On a previous trip in early September, my girls fought over turns in the stroller just for the shade.
You know your son better than anyone. I do think as kids get older, it is worth seeing how
they actually feel about a stroller. Some may be really opposed to riding in one; some may love the idea of being pushed around for a few breaks since they never get that opportunity at home. We've seen plenty of older kids in strollers when we've been down there and you should do what you all think is best for them. Yes, there is a LOT of walking at Disney, and certainly far more than the majority of kids (and adults!) do at home, but unless you are planning to run everywhere from open to close, your son should be capable of doing all of that walking with breaks.
If you decide that going without a stroller is the best choice for your family at the time of your visit, then you absolutely can do it!
For us, not having to haul the stroller to the parks and worry about parking it before rides and shows and then finding it again afterward (which we had done on our previous trip when the kids were much younger), plus finding larger spaces for parades and night shows to fit our whole party with a stroller, was great. As for ease of touring without one, we don't typically carry a ton into the parks and don't typically make a ton of large purchases each day. I carry a small cross-body bag and my husband carries a small backpack and we've found that to be amply sized for carrying around a few park essentials and purchases. Our rule is that if our kids want something larger than can be worn or easily carried in the backpack (or by themselves), they need to wait until we're getting ready to leave the parks to make that purchase. We also don't bring food into the parks except for a few small emergency snacks, so we don't need to carry around a cooler or anything like that.
My advice is to talk to your son about what he would prefer, think honestly about the storage needs you think your family will have for your time in the parks, and then make your choice. Either way, you will make it work and you will have a great time.