My chiropractor teaches that aches and pains don't come with age; they come with misuse over time. You have a little pain in the leg or back, you use the other joints to keep the weight off the soreness, and voila! you've thrown your entire sacroiliac and pelvis out of joint.
Although there are exceptions, many of the people with joint pain, particularly knees, are quite overweight. And they don't equate the extra 30 or 60 pounds of pressure on their joints with the pain.
It may not be a cure, but losing weight heals lots of aches, pains and even what doctors call 'aging diseases' like high cholesterol and diabetes.
Before you have surgery on those knees of that back that's been bothering you, why not drop some weight and see what happens. You can always use surgery as a last resort. I'm betting it's avoidable!