Many, perhaps most, older dogs end up with varying degrees of arthritis, so you are not alone.
My personal experience at the moment is that I have an almost 15 year old, William, with fairly mild arthritis. I make sure he stays very slim. Any excess weight will make life more difficult for a dog with arthritis. By slim I mean that when viewed from above he has a noticeable, but not exaggerated, waistline behind the ribs and in front of the hindquarters.
I'm a raw feeder and personally I believe that his raw diet also helps, but I know there's only anecdotal evidence to support that. Nobody has done any scientific studies as yet. He isn't on any medication because he doesn't need it at the moment. He has a very strong glucosamine and chondroitin supplement called Riaflex with his breakfast every morning. He still enjoys about 40 minutes off lead in the New Forest every morning, mainly at a steady trot or walk nowadays, although he can still break into a run if he smells a nice horse poo snack somewhere nearby
My friend's Golden Retriever, Ruby, was much the same as William is now by about 10 years old but became worse and eventually needed daily meds to help her. I know she was on Metacam for a long time, and other meds such as Pardale (a paracetamol based pain reliever at other times). Metacam and other meds. can do damage to internal organs eventually, but if they're needed, as they were with Ruby and probably will be with William, then I wouldn't hesitate to use them along with keeping the dog slim and adjusting exercise as needed.
Lovely Ruby lived until she was 15. She could only do short walks in her last couple of years but they were mainly off lead, because she self regulated and didn't overdo things, so she was still walking and sniffing around and just being a dog and enjoying herself, just at a much slower pace and for short periods. Her owner also used to take her to garden centres and dog friendly coffee shops to give her a bit of variety in life and keep her mentally stimulated. So although I'm sure that not being able to do long walks is disappointing for both of you, there's no reason why you can't still go out and about and do a variety of things