Here's how your skin changes:
up to age 15 ----- smooth textured skin, pores small
15-25 ----- Acne, fine lines start to appear, pore size increases
25-45 ----- first wrinkles, early signs of sagging near eyes,
some loss of elasticity, adult acne
45-55 ----- more wrinkles, rough texture; sallow skin tone; pores
and age spots enlarge; sgging near eyes & cheeks
55+ ----- Wrinkles & fine lines in abundance, uneven pigmentation
sagging worsens, dark circles under the eyes
(taken from "the world of skin care" - olay -
PG.com)
So at age 28 if you don't have any of the above signs of skin changing -- I'd start preventative measures anyway.)