I think I should have sex at the age I am now. I think I should start having sex at 17, the age I did lose my virginity.
I think you should have sex no earlier than age 17, when you are ready and capable of handling the physical, emotional and psychological consequences of having sex. Not to mention being able to handle the financial consequences of having sex (purchasing birth control, paying for doctor's appointments, taking care of pregnancy or STIs, etc.)