Adult males actually have longer tails than females do, at least this has been my observation. It's a very minute difference, but one that I have noticed. When they are young and before their first molt, they have female coloration, so if they have shorter tails once feathering out for the first time, that wouldn't surprise me. They wont start their first molt until AT LEAST 4-6 months in age, although it could be as late as 12 months in age before the first molt into adult coloration. Being that your cockatiel is a pied, he might not change too much in coloration. He may even keep his "dirty face" for life, because he's pied.
Cockatiels are sexually dimorphic, but pied is one of the anti-dimorphic mutations out there, meaning that other factors may be required to identify the gender of the bird. From the sounds of it, you do have a male though!
The three cockatiels I posted pictures of are all females (not counting the male in the background of the first image). The pied hen (middle tiel) can also wolf whistle.
BTW, here are close up pictures of Casey, the third hen's face!
I like her little hairs!