which science diet formula?

What's the difference between the science diet "feline adult" formula
and the "senior" formula? I'm talking about the dry food that comes
in the bag. I've continued to feed my 11 year old cat the "adult"
formula despite the label saying it's for cats under 7 years. A vet
some time ago told me it didn't matter, but that was a few years ago
and am wondering if I should change. Thanks.