Cats know about other cats by smell?

Every time I go over someones house who has a cat and come home, my 2 cats are always smelling me. It's funny, but they tend to smell me more if I go over certain houses, as if certain cats interest them more.

My question is; by smelling, can my cats tell the age,gender,health, emotion, even breed of the cat from the other house?

If i'm brushing a cat at the house, and come home, do my cats know I brushed that cat by it's scent it gave off? (in other words a happy scent)

I doubt they could tell breed... The rest is likely though, age if the animal was sexually mature (and not spay or neutered). Otherwise I don't think they care too much about age. Your cats are probably wondering why you're coming home smelling like strange cat when you have them waiting at home for you and not so much what the other cat was feeling at the time you were petting it.

But do you think they can tell the mood/health of the other cat by smell?

I heard strays smell this type of scent, and sometimes a cat will mark the area with it's scent to tell other cats if the area is safe or not. I would imagine a sick cat would give off a different smell whether there fixed or not.

I can't say this is 100% true, but I do know that the day Lizzie got so sick and we had to have her PTS, her Sister Gracie...who was her very best friend...won't go within 10 feet of Lizzie, and even at that Gracie would walk by a hiss at her.
Never in all the time we had them...7 years...had Gracie hissed at her beloved Lizzie.
So I do think that they can tell if another cat is sick...Gracie sure knew Lizzie was.

Yes, same with dogs. Smell is an important "newspaper" for animals. That's why most cats hate the "new" cat that comes home from the vet and hiss/growl and avoid him/her till they smell normal again.

Most cats probably don't tell the breed; however my cornish rex hated to be around or near devon rexes. Apparently the devons have a different odor to them compared to other breeds. Spooky was fine with any other cat in the show - wouldn't give them a 2nd look. But if there was a devon nearby or next to him in the ring, he would search out that cat and hiss at it! Every time.

We could not put him next to a devon in benching or in the ring - he had to be separated far away.

Thanks for the information everyone it was very helpful!