Exercise is probably the best thing you can do to improve your longevity. I don't have a source, but I don't think this is a controversial idea. Even long walks can help (though as someone who lives in the middle of nowhere, I can understand if this is not possible). I'm only 28, but I find that long walks on the treadmill (with my laptop in front of me, while I'm working) can really make me feel a lot better. I do have a general fitness routine I keep up with though, so that likely plays a role here.

One thing that has helped me immeasurably is taking up a hobby that gets me outside and doing some manual labor. I love gardening and I'd suggest it to anyone. I have shed several inches off my waistband since starting to garden and I find myself spending considerably less time in front of the computer screen just wasting time.