I hardly ever bother with my cat's nails anymore. He doesn't scratch inappropriately and cause damage outside of the door trim, which is a non-issue for me and can be easily replaced or filled in when the time comes. With the younger, playful kitties, I'd say 6 to 8 weeks sounds about right or whenever their claws cause injury or they climb the drapes or your pants.
I do it myself. I used to be a vet tech and groomer, so it's really easy and quick for me. I wrap the cat up in a blanket like a burrito to spare us both from injury, and cats feel more secure if their heads are covered. Cat nails are really easy compared to dog nails, especially black nails, so I get through the process pretty fast. If I find his nails hook to the carpet, which is rare, or if I feel like some cat wrestling, that's when the nails get cut. My cat only pays attention to me when he's hungry. He's the most antisocial cat I have ever had. I would probably trim his nails more often if he was actually around and might poke me with his claws.