Sorry to hear he’s struggling - it sounds pretty typical of an older, arthritic dog, but I agree he is too young for this!
All of my dogs take joint supplements (glucosamine, chondroitin, MSM, and hyaluronic fluid) from the time they are “middle aged” at around 5-6, so before problems usually start. I have no idea if they help as I don’t have a control group, LOL, but they don’t seem to hurt.
Scully also had acupuncture which did help a bit, as well as Deramaxx and we eventually added Tramadol to the mix. Gabapentin would have been the next step for her but she never needed it. The best thing we did for her was to get her swimming as much as possible - it allowed her to build strength and some flexibility without added stress on the joints. Even so, slow walking was just a way of life her last few years. She had bad elbows which started being a problem around age 8 or 9.
Mulder was on the joint supplements, and around when he turned 14 we put him on Rimadyl for some arthritis in his hips. Swimming didn’t help him though, as he had arthritis in his front feet which never seemed painful, but prevented him from spreading his toes and swimming effectively, which made it too much of an effort for him. Again, slow walking became a way of life as he aged, too.
I find that for the old dogs, several shorter slow walks seems to be better for them than one long one. Either way though, they are slow. When we have had older dogs with younger ones, we have had to go on separate walks as what works for the older ones just isn’t enough for the younger.