How old does a female kitten have to be to get fixed?

Kittens as young as 8 weeks old can be spayed or neutered. It's not really necessary to have it done THAT early, but keep in mind that cats can start having babies as young as 4 months old. So don't wait too long!

Also, getting it done when the kitten is still very young -- like 8 to 12 weeks -- is supposed to be better for their long-term health.