Our cat is 4 and we don't regularly use any treatments. She's always had a clear bill of of health at her annual check-ups and has never, to our knowledge, had any flea or worm infestations (I've looked up symptoms and she's never shown any of these).
From reading around though it seems like you're meant to use treatment every 4-6 weeks, is this what everyone else does or do you only use treatment if your cat is infested?