so how old you are depends on what you need to do with your skin, and how you need to look after it. though we can't turn back time. it is best to start at a young age so if you can start early.. if not, well dont think that what you do now won't help cause believe me it will.
20s - the most important thing to do at this age is SUNSCREEN. so start protecting your neck, hands, chest as well as your face. If you're likly to stay up all hours of the night drinking and smoking, kick start anti aging by using a serum at night that contains vitamin C to help fight free radical damage.
30s - as you get older you skin only exfoliate every 35 days naturally instead of every 14 in your 20s. so this is why its important for you to exfoliate two to three times a week. If you have drier skin, twice a week is fine, if its more oily, then three times a week will help. Add a retinoid to your skin care routine at night to help improve your overall texature
40s - lines of movement aren't going away as easily as they did in your 30s, so you'll need to add moisture and collagen-building ingredients into your routine. Peptides is an ingredient group that is helpful to rebuild collagen assisting in hiding those lines.
50s - Loss of tone and sagging are the biggest issues, consider talking to your skin care therapist about laser treatments and other non-evasive or evasive skin rejuvenation options. Ensure your using a peptide and retinoid.
As you get older, don't take away the fact you need to use sunscreen. You should be protecting your skin and your children's skin from day one, this will be your best tip to slow down the aging clock as well as avoid skin cancer.