The younger the better I say. They will be able to get used to you handling them and clipping their claws. When I got Miggy and Petal, both 2 years old, they had never had their claws clipped. You'd think I was murdering Miggy for all the noise he makes now when I clip them. I have to wrap him up in a towel to do it, but it's over very quickly, thankfully!
I buy my soft claws at thecatandkittenstore.com
. I can get soft claws there cheapest I've seen, plus free shipping. It's cool.