Here is my experience with aging knees. When I was in my 20's I regularly carried 60 pounds (90 days each summer- I weighed 115 pounds) and had no problems. My knees started to get a bit creaky in my 40's. My wonderful daughter backpacked with me and taught me a lesson- she was a steady but slow hiker and with the same pack weight, when I slowed down, my knee problems went away! So it was slow and steady, break every hour. In my late 50's I started using trekking poles. THis is another great change for those of us who have aging knees. Also, all throughout my life I have never let my weight vary more than up or down 10 pounds. This summer (at age 60) I did a 12-day trip with a fairly heavy pack (45 pounds)and did not have knee problems. For me it is not the weight of the pack per-se, but a lot of other factors that make a difference on my knees. One reason I hike alone more now is that when my knees start to hurt, I do not push it - set up camp and rest. As I get older I need more rest time between stressing my knees. By the way, I quit long distance running in my 30's because I felt that I would rather have my knees last for a lifetime of backpacking.

So I would say to Swimswithtrout- go for the long trips (there is really nothing like being out 30 days straight), listen to your body, schedule in enough rest, use trekking poles and go for it.