IAMs 7+ year old cat food?

I looked around on the package of IAMs "7+ year old" cat food and did not
see a description. Well, now that I think of it, they probably have a web
site, hopefully that would be on it.

But just in case they do not.

What is that food for? Apparently for 7+ year old cats. My problem is that
I want to give them the hairball formula and at the same time a low calorie
food.

I do not see any comments on the thrust of Purina's Indoor Cat Formula. My
guess is that it would help with both of those. They usually are less
active, and they do not have a chance to eat grass or whatever other fiber
rich substance.

I guess my cats will continue getting the hairball formula and I will just
have to ration it.

I vaguely recall reading that cats should have dry food left out at all
times. Is that a common recommendation or could I have confused that with
advice about fresh water?

Thanks in advance.