When Can A Kitten Be De-clawed?

First try ALL other options, and if none works --- do your homework in choosing a GOOD vet with lots of experience in the proceedure.  Ask to talk to those who have used his services; get their feedback on the results.  Just like any "professional", veterinarians come in all levels of capability.
Claw removal can be excruciating or just mildly uncomfortable.
Mine were declawed at about 1 year of age, well after being spayed & neutered & had no problems.
My oldest is over 19 years; she is the litter twin of the other that was declawed & the only 2 cats, out of MANY, MANY that ever had to have claws removed.
I tried every option you could mention, but...

Getting a cat de clawed is very cruel and over the years can harm the cat. The cat will lose its balance and pretty much have to learn to walk again. It also causes a lot of pain for them,  and they'll be confused as to why they can't climb or defend themselves. They also begin to not trust you. I highly don't recommend doing-if you still feel the need-i think about the time they are able to get fixed you can get them de clawed. But you will be paying a lot of money for it, and they may come back.