Have you noticed that some NPCs are clearly meant to be elderly if you look at their faces, but their bodies seem to be more appropriate for a younger person? Furthermore, this is not consistent - some older NPCs have bodies and faces that match.
Now, this may or may not bother you, but the visual disparity annoys me. What most people might have done is make the fake-old NPCs younger. Instead, I reckoned that generally the NPCs are supposed to be the age their faces look, so decided to make their bodies match their faces.
This mod requires that USSEP is installed, and your game will crash on startup if it isn't.