I'am 19 and i would like to know what can i do to have a healthy and beautiful skin , to prevent a little from the changes that comes with aging ?

Avoid the sun & cigs: Aging is natural and we all do it. Some age better than others though. The way to keep your skin healthy and happy is to avoid the sun and avoid smoking. Both will age the skin much fast than time alone. Get good sunscreen and use it daily - especially on hands and face.

Healthy skin: The single best thing you can do to keep your skin in great shape is to avoid sun exposure and to use daily sunscreen for the times that your can't avoid even a little sun. Most of the changes that we recognize as aging skin changes is really chronic photodamage.