If he's a boy, and has pearl markings like Muffin on his back and wings........you'll know he's a boy if he loses his pearl markings after his first or second molt. If he keeps them, then most likely, *he* would be a *she*, because female pearl cockatiels normally keep their pearling for life. Baby tiels often have tattered tail feathers, so he/she is probably young. Where'd you get him from?