If you want to test how elastic your skin under your eyes still is, perform the following experiment (though it's admittedly quite ruthless): pull your lower eyelid down so that the whites of your eyeballs show. And then quickly release it. Does the eyelid immediately come back into place and fit snugly against the eye? Then congrats, you are still fine! But if it doesn't happen right away, much less with a delay of two seconds or more, then you've probably fallen victim to one of the factors that speed up aging.