It's never too early to start using a high-protection sunscreen! That is the most important anti-ageing treatment - Prevention!
The UV rays of the sun cause premature ageing and the damage starts in childhood.
Proper cleansing, gentle exfoliation, organic oils (I see you are already interested in them!) and good nutrition and health habits are a good place to start.
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.)
Personally i think 25 is too young to be anti aging, yes get in good skin care habits but however anti aging products are strong and you need to be careful what you use at such a young age!
Yes though 28 is good age to start taking care of your skin! Start off slow cleanse, exfoliate and moisturize, Spf too is important every day, and then introduce anti aging products Vit c serum and so! Dont though do everything at once this can also damage your skin!