For really fine wrinkles, pores, and other uneven skin texture, I’d go with texture painting instead of trying to sculpt it.
(I recommend the trunked Image Layers Addon (http://cgcookie.com/blender/2011/10/18/using-the-texture-paint-layer-add-on/ ) and external Image Paint Plus (https://sites.google.com/site/bartiuscrouch/scripts/texture_paint_plus) for any texture painting).
Pixel-level details are far ahead of what you can realistically work with in Blender’s sculpt mode, and GLSL mode handles real-time bump maps wonderfully.
A great little trick both when sculpting and painting, is to use Stroke->jitter&spacing to get random painting patterns without messing with texture masks. Combined with different falloff curves, this gives a lot of creative possibilities.
As for the wrinkles themselves… google a lot of reference images. If you want directions, check into Zbrush tutorials. There’s a lot of messing around with That Interface, but the sculpting itself tends to be really high-level.
I miss some definition around the eyes, but other than that it looks like a great start.