hahah... lol this thread makes me laugh so much... At 18, I wouldn't expect anything bigger than what you got. 6 inches is normal all over the world, and honestly I get lucky when I hit 6, I'm just shy on certain moments
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If you want to know the truth about it, use the net. WebMD has great info, hell even check wikipedia, theres lots of peeps out there who do the research and try to keep wikipedia up and running properly without any false information. From what I've always heard avg is 5 1/2 to 7. Thats a big gap when it comes to every mans thought of their dick size. (Don't listen to people on the net, e-peens are always bigger than real peens.)
My personal advice to you is to just get the idea out of your head while you, rid yourself of penis envy and be happy with what ya got. All those other guys were fucking with you, so seriously, don't worry bout it and remember. You have a tongue, fingers, and many other ways to make your woman have a great time, it doesn't all have to be focused around your cock.