I read a great post by Best Bully Sticks (@bestbullysticks on Twitter) talking about caring for your senior dog. In this post they mention the importance of taking your dog to the vet, not only when your dog is sick but at a time when they are healthy so your vet has a baseline to use to compare results to down the road should your dog become sick.
I have been through this exact same thing and trust me it does help. Before I was able to put my 13 year old Pug on Medicam, he needed blood work to make sure his body could tolerate this prescription. When the blood work came back they compared it to a test he had a couple years back and discovered that he had some issues with his liver that weren't there in his last test. We were able to address the liver problem and Mackenzie is now safely on Medicam and happier than ever.
Another important point mentioned was the need to keep your older dog active. I have spoken about this before and I think it is worth mentioning again. What tends to happen, and I know this because I went through this myself, is that as your dog gets older and starts stiffening up, you stop walking them. In my case I even stopped taking Mackenzie to dog parks. Then I realized that by doing this I am actually accelerating the aging process.
Old dogs still need exercise for physical reasons, but also for mental stimulation. What I often recommend is using some of the wonderful products out there to become creative in how we manage this side of our older dogs life. For me I use a dog jogger and Mackenzie comes on long walks and visits dog parks and all along the way he goes in and out of the jogger. So he gets the right amount of exercise and an abundance of mental stimulation. He is still an adventurer and loves to explore, I just needed to find the right way to let allow him to do this in a healthy way. Our senior dogs still enjoy all the same things they used to love when they were younger and it is up to us as dog owners to find ways to let them continue to enjoy life