16-18 you should be done... atleast that's how it was for me. I've been the same size since I was about 16 or so and I'm 21 now. Don't get too down on yourself though if your not happy.
Number 1 if you havn't had sex yet then how do you know you're not good enough
Number 2 if you are comparing yourself to pictures on the internet, take note that they are about the top (generally) 2% that's out there, and the women they are having sex with are used to (and some times apparently bored with) that size... The average vagina is 4 inches deep and stretches from there.
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