Yes, its normal at 16 and the sad truth is that its getting even younger than that. I like to compare sex to candy. Remember the first piece of candy you had? Well remember that after that you wanted candy like every day until one day you just didn't and it eventually slowed down until you would have candy once in a while? Same thing with sex. You don't know about it until you tried it. Once you had sex and lost your virginity (aka your friend) she'll continue to have sex like it was going out of style and the world depended on it. Eventually, she will get tired of it and or realize that sex isn't everything and the crave will go away if only for once in a while. Like the candy example. Hope this helps!