Yes - I always had insurance for my previous two cats Tom and Sophie - they were incredibly healthy until Tom's FD/acro dx and that cost the insurance company a good few pounds, although I had an "excess" on the policy which meant that I had to pay the first 15% of every claim, or similar.
I've had insurance for my little civvie Sapphire since she was nine weeks old. It's not cheap and goes up every year, but I reckon that veterinary treatment is so expensive that it's worth having the peace of mind that comes with insurance. At least then I know what the monthly cost is, as opposed to a possible nasty shock if she was to need treatment in the future.
Some people "self-insure" which is basically putting a sum of money aside each month, maybe into a separate account, which would be used to pay for or go towards vet treatment. If you have a young animal and don't need to visit a vet for several years this can be a good option although as others have said above, older cats cost more to insure because they are more likely to develop conditions needing treatment as they get older.
It's probably worth ringing round for some quotes (actually speak to the staff instead of getting a quote online) - you may find something that fits the bill. Good luck!
Diana