Young Leghorns are notoriusly difficult to sex. Pullets who are at POL can really grow an impressive comb and wattles. The tail on this particular bird looks girly. Give him/her more time. Of course like the other poster noted if this bird is greater than 4 months start looking for eggs!
idk about everyone else but i see roo. i disagree with above post. a pullet WL would show more tail and would be a bit more extended but flat even . this taail looks very boyish to me actually. it looks to be a roo. my leghorn pullets dont show their combs or wattles until 4 months almost EVERYTIME. but id like to see the results to this with time. keep us posted!