please do not wait until a kitty is 6 months old to spay- by then they can already get preggers and have kittens!
at the shelter i work at we spay at 2lbs. We always have great success with our pediatric spays and all of the kitties seem to recover well at that age as well.
A kitten can be spayed as young as 8-12 weeks of age so long as they weigh at least two pounds. Any lighter and their reproductive tissues are very thin- like rice paper, so it's more difficult. That being said though- i have seen kittens as small as 1-1.5 lbs spayed in a rare emergency and they recovered just fine! When we put a kitten under anestesia that young, we give them an injection after their surgery to help them wake up quicker. Kitties (no matter what the age) tend to take a while to wake up from anestesia- so when they're that small, we just help things along by giving them a small injection to wake them up quicker.
Never had any problems from it!
Also- when you have your kitty spayed- be sure that they tattoo the spay site so that if she ever gets loose...a shelter or vets office can shave her tummy to check for a spay scare and KNOW she's been done. Sometimes spay scares are very hard to see- especially if the vets done a tiny incision (such as in a pediactric spay) and it is not tattooed. All the tattooing involves - is after the kitten has been stitched up, they will take a tiny needle with tattoo dye in it and put the dye into the incision site. (kitty won't feel it as it will be under anestesia.) At my shelter we use teal green, at the other local shelter blue and so on -so that if an animal turns up in our shelter, we know what shelter they were altared at and can often locate the owner/files
Many vets offices now offer this as well as do low cost spay/neuter clinics. If you want to have your kitty microchipped- go ahead and have them do all vaccinations and microchipping while the kitty is under anestesia to not stress the kitty out since it will be asleep. Be sure to keep the kitty in a nice warm quiet place for about a week after you bring it home until it has its stitches out to reduce the chances of it moving around too much and tearing the stitches out. Also - when we spay younger kittens -we opt to use regular stitches, not disolveable ones - because on occassion we like to keep them in a few days longer depending on how the kitty is healing- with disolveable ones you really can't say. So regular stitches should be just fine- they will need to come out in 7-10 days. (takes about two seconds to take them out, i do it all day long at work, and it doesn't hurt them at all
So definitely go ahead and get your kitty spayed- it is more than old enough!