Board Thread:News and Announcements/@comment-6697950-20140102180802/@comment-6697950-20140419094121

However, I have heard that, because the identification of the players' sex occurs due to the players' brain waves, in extremely rare cases, due to some impulse the system decides with the opposite sex, players have been startled when they dive in.

A few lines after this, the guy asked for Kirito's play time:

"Gossip then, that rare avatar seems to have been used for a long time in a previous account. As a reference, can you count up your previous account's play time for me?"

It doesn't specifically state that the player's game time is tied to receiving this avatar.

And by "could not decide which gender Kirito belonged to", I meant that the system had trouble figuring out which gender he should be assigned to and it ended up choosing a feminine male avatar. That sounds like a compromise to me.