I can’t remember how old Scully was when she went on it (bad elbows), but I want to guess 8 or 9? She lived to 15+. We did lose her to kidney failure, which may or may not have been caused by long term Deramaxx (and eventually also Tramadol) but at that age, it might have happened anyway.
At a certain point, you have to weigh longevity with quality of life and I can tell you for sure that without the Deramaxx she wouldn’t have been able to have a comfortable life for as long as she did so even if it did hurt her in the end, I think it was worth it.
By the way, having parents with good hips/elbows increases the chances of your dog being okay, but it’s not a guarantee as inheritance is very complicated and environment (weight, exercise etc) plays a role as well.