It has been said that the greatest amount of damage done by UV rays is that received before age 20. Research definitely indicates that over exposure to the sun's UV rays during childhood significantly increases the risk of developing skin cancer later in life.
The teen years see the most high risk sun exposure. Out of parent's watch, and insistence of sunscreen usage, teens are much more likely to get sunburns and sun damage. And this is not only happening at the beach and pool, but tanning salons too.