It's not just the texture.  The main problem I see with "mature" characters who aren't is the facial features.

The ears and nose continue growing throughout life: while the ears you can get away with, a female character in their late 30s and on is not going to have a cute little nose but a larger one, and it gets bigger with age.  The eyes shouldn't be so large in the face.  The facial features and head shape shouldn't (except in some cases) be so smooth and rounded.

In terms of bump or displacement, lines at the corners of the eyes and around the mouth.

It actually doesn't take that much.  I'm at work right now and can't whip out a render, but I have one character who uses a plain female texture map (nothing in it specifically meant for a "mature" character") who looks older than a typical poser female because she's got a prominent nose, a hint of wrinkles around the eyes, smaller eyes, and defined creases at the corners of her mouth.  That's it.  My main problem with her, in fact, has been dialing back the apparent age.