It's interesting to see how Cooper is aging at 11-12 years old. At home, he's stopped jumping up to put his front paws in my hands when I asked him to. His hind legs are clearly slipping more and more when he sits on the hardwood floor. You can tell he's stiff and achey sometimes, and when you're massaging his flanks, you want to be gentle.
On a hike, he can run up a vertical creek washout and propel himself over the edge. When Loki (3 years younger) is pooped and trailing us (stepping on my heels the whole way), Cooper is jogging ahead, looking back occasionally, seemingly wondering why we're so far behind. Still dashing hither and yon to check out little noises and smells. This is on a six mile trail, or who knows how long in off leash dog miles. It took us almost four hours, about 45 minutes of which was sitting at a creek, but we humans were hobbling along after an intense gym workout the previous day.
All dogs are not built the same. Loki has had some sort of hind leg gait issue for years. We've tried all sorts of things - CBD does help so that he's not crippled for two days after a hike, but he's definitely gimping around this morning. On the hike back, he was noticeably drained. He only dashed forward a couple of times.
We leashed the dogs for the final uphill approach to the trailhead. Neither dog was any use in pulling us up the hill, so clearly they both have aged.