Two points, bobone:
The cocks on this site tend to be way above the average that you'd find out on the street. That is, after all, the entire point of the site. Not everyone out is as big as the boys on here.
If it's your first time with a man, perhaps you should concentrate on finding someone you are attracted to, and who you can trust to take you through it all gently and respectfully, regardless of the size of their penis. If you just go for the biggest dick you can find right off the bat with no preparation, then it will hurt and then it'll put you off for the future.