If your knees or back are going out in your 30s you're likely either fat or inactive or both. Lose weight now, get active now, joint damage is cumulative. (Yes, hard labor will jack you up, but not that young. And some people are just genetically unlucky. I gather being tall is bad as well?)
Read a great quote years ago, "How active you are in your middle age determines how active you will be able to be in your old age."