Sex is one of those magical things that, when asked what time is good to try it, has many answers. It is personal, the decision lying on your shoulders. Yet, do not rely just on your physical wants...you will be confused. Hormones will urge your forward, but in reality people are not mentally mature enough to be sexually active until their early twenties.
16 may be the legal age in your state, but I think not giving in to your ex's pressures was the best thing you could have done. You have so many years to grow and mature, to better comprehend what that act would entail.
On another note...You were right, he was wrong. It sounds to me that boy did not respect you, both because of his persistence in what you had already told him no to, and in turning to someone else to get just that in spite of your "time limit."
You are not a cold fish. One of my dearest friends told me "Make him earn everything you give." And that, my friend, is something quite costly that any boy will need to work for. Sex is something special, not to be hastily given away. I hope that helped, please keep us updated! (through here or pm)