Do cats eat less as they age?

I'm not sure about this...I've noticed my 3 girls have seem to cut down on the amount of food they normally take in. Is it because of age, or are they just sick of the food? It can't really be the latter because I make sure I change the flavour with each bag of cat food that I purchase. Could it be because they're upset too? Or is it that their tummies and appetites have just gotten smaller?

I haven't weighed them for a while already, too. The last they visited a vet was more than a year ago. They had their vaccination done at home so they weren't checked on their weight. I feel that they have gotten a little light when I picked them up...which is not surprising seeing that they didn't eat as much nowadays.

I'm not too concerned at the moment because they don't appear to be ill. But if they keep cutting back on food continuously, maybe it's time to have them checked on. You reckon?