Both my cats are neutered / spayed.
I had Phoebe spayed when she was about 14 weeks old - I was so paranoid that she would go into heat and have kittens (she's an indoor / outdoor cat). Kelvin's previous owner had him neutered.
My 2, Duke & Cosmo, are 4.5 months old & brother/sister. I have an appt for them Monday but the vet won't "automatically" schedule the neuter/spay until he sees them. They initially told me they were too young and to wait another month, but I assured her Duke's "parts" were very clearly visible LOL so she made the consult appt for us.
I got Lucas when he was 1 yr and 1 month old and he wasn't neutered. Got him on a Friday, Monday he went to the vet to be neutered. Besides, here in VA the law is that when you adopt a pet from the shelter you have to neuter/spay.
Both my boys are nuetered, both were around 16 weeks when it was done. I've always had altered pets so it was a no brainer. They're both domestic short hairs, mutt cats but they are beauties that for sure. But I don't want to add to the unwanted pet population.
That being said, I am considering starting a cattery in the next 5-10 years with British Short Hairs so if and when I do that I will have unaltered pets. I'm currently researching as much as possible so we'll see how it goes. I have a lot of research to do, I like to be fully prepared and educated before I start any venture. By then I will also hopefully have my own house instead of an apartment. We'll see though, I may change my mind between then and now.
Sophie was already spayed when we got her from the Animal Protective League. Angel was apparently caught in the TNR program before she found us. Her ear is tipped and she is definately spayed. Percy is neutered, although he wasn't too happy about it!