Looking after your skin through the decades is about ensuring that skin is always repairing and re-growing faster than it is degrading,  and part of that is ensuring a really good skin maintenance regime is in place to protect against the daily stress our skin undergoes.  
Regular removal of the cellular debris that causes damage in the body is the best option for ensuring  you get the maximum mileage out of your skincare regime. “Cleanse, tone and moisturise” is the Nourish mantra for every age group. This, combined with a healthy diet and regular exercise will ensure your skin stays looking younger, for longer.
In your twenties, always keep your skin topped up with antioxidants, and get into the practice of using products that contain antioxidants, (like vitamin c,) as this will ensure your skin has a reservoir of active ingredients to help ward off environmental damage. During these years the balance of growth reactions to degrading reactions within the skin is still very favorable, and as long as good practices are in place, skin maintenance should be relatively easy. If you are indulging in a lot of late nights and drinking heavily, be sure to take regular supplement of milk thistle and B vitamins.
In the your thirties the most notable changes in the skin are a reduction in the level of ‘water soluble matrix components’ such as hylauronic acid and glycoproteins. At this point it is important to start ensuring your moisturiser contains ingredients to support these water soluble components, such and vitamin b. Regular exfoliation should be added to your skincare routine. 
In your forties the level of estrogen in the body begins to decline, and this is accompanied by a decrease in epidermal lipids. At this stage it becomes more important to supplement your skin and diet with omega 6 and 9, as these are oils that the body cannot make for itself. The addition of a facial oil to your skin care routine is also highly recommended. 
50s and +
In your fifties collagen and elastin decline start to become more significant, and visual signs of ageing can become more prominent. Having a regular routine that incorporates exfoliation and facial oils is a must.  Look out for ingredients such as rose of Jericho, which help protect the vital enzyme systems within the skin, and ensure regular use of moisturisers containing vitamins C and B.  Facial acupuncture has also been shown to help stimulate rejuvenation.