I like my elder ladies to use the elder skins, but I hate the exaggerated body shape. So I edited the nude top, bottom and full-body meshes for elder females. As you can see, the shape is still noticeably saggier than the Maxis adult, but not nearly as grotesque as the standard elder, and the shadows are pretty much where they should be (which unfortunately is not the case if you solve the problem by using the adult nude meshes for elder ladies, unless you also alter all your skintones and essentially make elders identical to adults.)
Only the high-def female meshes have been changed here; they won't affect Sims in a game set to low detail. Also included is a mesh replacement for elder males by Zirconia Wolf at Simbology (included by permission), which makes the elder males use the adult meshes; this is more practical for men, since there's less difference between the male adult and elder meshes and the boob-shadow problem does not apply.
As a bonus, this will also work for any swimsuit or underwear that uses the elder female nude mesh. Downside: Elder tops based on the nude top mesh will no longer match up with standard elder bottoms. :/
I'm still fairly new to body meshing, so this isn't quite as perfect as I'd prefer, but it tested pretty well in my game. If anyone has problems with it, please let me know.
Author