Latex

No, no, no before you think it, its not that kind of latex.  Glad we've cleared that up! 
So anyway, this is another aging technique using liquid latex. The process involves (amongst other things) stretching the skin and layering liquid latex onto it.  When the skin is released the latex helps form creases from the stretched skin and these look very much like wrinkles.  The end look can be very realistic when teamed with the shading & highlighting technique.

say cheese you've just aged 10 years!