It is best to declaw kittens when they are fairly young because they will recover more quickly. It is recommended that the kitten is around four months or older before getting declawed. Some vets will declaw the cat at the time of the spay/neuter surgery. For more information about declawing, you should check this site - http://www.talktothevet.com/ARTICLES/CATS/catdeclawing.HTM
A kitten should be around 8 to 16 weeks old when becoming declawed. The declawing may be harmful to a cat at an older age, so it is better to do so when they're younger. Many vets will not declaw a cat if they are over 5 years of age. In most cases, only the front paws are declawed so the cat will still have some means of defense and support.