Neither Male Nor Female Lloyd in Space : Season 3 Episode 9

The boys and the girls make a bet as to the sex of the new kid, Zoid, but Zoid comes from a planet where you are neither sex until your thirteenth birthday when you can choose it. When Zoid's thieteenth birthday does roll around, he or she refuses to reveal it. The only way the gang can ever find out is if Zoid gets a crush on one of them.