Oh yikes, that sucks. I've had bad (in fact, awful) knees (both of them!) since my early 20s (a combination of work, exercise and dancing did them in long before their time was up) and have more or less lived around them, but everything else stayed OK until I lost dependably pain-free use of my foot at 43-ish (it got crushed under something).

That, more than anything, took me down. 3 years later my foot's pretty much stabilized, but as a result of long-term limited use of it, everything else is pretty much falling apart. :)