I don't know of a tutorial but here's a couple of thoughts.

1. An older face has more wrinkles, and quite a few models already have morphs available that do that.
2. The skin texture will typically have small, dark patches, often called "age spots" or "liver spots". The skin will also typically not be clear in other ways, possibly including uneven tanning, scarring, freckles, and so on. Careful work in a paint program with your textures may improve the aged look.
3. Cartilage continues to grow throughout the life of a person, so the nose and ears of an older person are usually larger than in youth. If your model has morph targets for these areas, you may improve your look with them.
4. Everything sags with age, so the cheeks, under eyes, and forehead areas all droop a little bit compared to youth. Also, many people go through a weight gain in middle age and drop the weight in later years, creating extra skin around the under-chin and cheek areas. Magnets or morphs may help with this.
5. Many older people adopt a bit of a squint in their eyes as a reaction to failing eyesight. Also, it is not uncommon for there to be some hazing or yellowing of the cornea.
6. Individual hairs get thinner as a person ages, causing the hair to lay more flat and be a bit more lifeless, in addition to becoming gray. You may want to look for hair that does this, or take it into account when you paint your hair on after rendering.

Hope that's helpful.