Supposedly one's metabolism changes every seven years. I don't know if that's true. I do know that the past year and a half has seen me gain more weight than I'd like. I'm blaming the constant barrage of bagels available at work, so I'm going to stay away from them for awhile and see if my weight goes back down to a more comfortable range as quickly as it used to do.
My skin is still its oily self, though I get less acne than I used to. I still feel strong, but I wonder if I'm as strong as I was seven years ago. I'm more susceptible to colds/flus going around, so I get a flu shot every year. My night vision is going downhill, but that's probably due to general age anyway(I'm in my early forties).
I think for women the biggest changes is when they start and stop menstruating. The hormonal effects on the body in those cases are remarkable.