screwsandpllates, i think it's a combo of things.
do you have a negative under eye vector? That is, like the girl on p. 330 that Jaws posted you can see that the under eye area is not supported by a strong orbital rim or cheekbone. This can lead, even in young people, to mid-face ptosis: drooping fat pad. I think it also has to do with your tissue quality, some people's skin is more taut and elastic, other's thicker and prone to drooping. You have a few options none of which alone will necessarily fix it. 1) a midface lift, if you're a girl that's good because if they do a full face lift you don't have the sideburn behind the ear problem and facelift's by good surgeons are virtually undetectable when healed. 2) you may still need under eye support to fill that area in, so then either a cheekbone advancement (however you want to call that, modified lefort 3, ZSO whatever)
Of course the latter alone may suffice. Without pics it's tough to advise of course.