I have had two dobemans that had arthritis realatively young, one is still here at 11, and the other passed away at 11.
Arthritis is harder to treat in a younger dog because it is chronic and can only be treated effectively chemically. You can control the inflamationa and pain, but there is no cure. Just like with people, what medication works today may not be as effective in two years.
Hip dysplagia in a young dog is easier according to most vets because it can also be managed in some cases surgically, with hip replacements, or chemical with pain control, glucosamine and chondroitin and other means.
But, the good news is that tina is right, there are so many new medications out there now arthritis in any age is easier to manage than ever before.
Stella