Your skin is an organ like all the other organs in your body, and unfortunately as it ages it simply looks older and less attractive. If you put extra stress on your skin, from sunlight, smoking, or bad diet, natural aging effects are increased!
When you are young, your skin regenerates every 15 to 18 days, but this slows down as you age. When you are in your mid 30s, this regeneration takes much longer, about a month, and by the time you hit your 70s, regeneration will take several months.
As you age, the epidermis layer of your skin becomes thinner. Collagen also breaks down and your skin simply becomes less elastic and wrinkles and saggy skin result. Oil production from sebaceous glands decreases and pores become larger and clog. Also capillaries and broken blood vessels become more visible, adding to the aged look.
These aging factors, called intrinsic factors, and simply going to happen. However we can control extrinsic or non age related factors. Extrinsic factors affect your skin significantly and can cause premature aging - if you let them.
Extrinsic factors you have some control over include sunlight, exposure to pollution, and smoking, all to be minimized if at all possible to help keep your skin younger looking or at least from aging faster than otherwise. Wearing a hat and otherwise covering up in the sun, avoiding midday sun, and using suntan lotion are all helpful, as is not smoking and avoiding second hand smoke.
Your skin will naturally age just like all the other organs in your body. You have some control over this aging via extrinsic factors, and no surprise but the biggest one is avoiding excessive sunlight!