I think the best and basic way to exercise for any age is to do some stretching and walking. Taking more of fruits and vegetables and drinking more water everyday, as this may help you detoxify your body (for the young and not so young).
However, for those who are over the golden years and you are not used to going through heavy exercises, you must see to it that you have an approval from your doctor before engaging into exercises.
As for young adults like 16 or younger, you can start living healthy by eating healthy and enjoy your teen years, when you get to reach around 20's, then you can start building up muscles and toning them.

