Adoption centers such as pounds will spay or neuter and 2 months when a kitten is adopted. I personally think that is too young, and if you have the choice, it should be done 4-6 months. If you plan on letting her outside, you should wait until she is spayed first, so there is no "accidents" because she could come into heat around 6 months.
These lucky kitten has a Human, to be their God, you are the Ultimate for them, do what ever suits you. You owe them, hence you have all the rights, spade, nudered or allow them to mate. Your decision is final, check out, what actually suits you, they are your subject, at your mercy, ill luck, I am not a kitten or I would have pleaded on their behalf.
***Edited By: shinyblackpit on 1/19/2012 11:01:11 PM*** Reason: removed link
It really depends on your vets opinion. It can happen as early as 6 or 8 weeks, but the latest you should get it done is 8. Do not believe the myth of them needing a first heat cycle... one heat cycle increases their chance of cancer and other problems, such as spraying. Also, when their younger they can recover faster, and the procedure is a lot easier on the dr. http://primecoloncleanse.org/