Texture is revealed mostly by lighting, not post-processing. To emphasize wrinkles and skin detail, use light from the side or at a very shallow angle across the skin rather than straight from the camera position. This raking light creates bright highlights on raised areas and deeper shadows in the valleys, which makes texture stand out.

Avoid direct on-camera flash, which tends to flatten faces and reduce visible texture. Side light or other directional light is much better. The exact hardness or softness can be adjusted to taste, but the key is direction: light coming across the surface, not head-on.

In post, black-and-white conversion can strengthen the effect, and gritty/contrast-heavy processing can add drama. Increasing local contrast, clarity, or similar detail-enhancing adjustments can help, but they work best when the texture was already captured well with good lighting. If the light is flat, post-processing has much less to work with.

So the basic recipe is: directional side lighting first, then moderate contrast/detail enhancement in post, especially for black-and-white.