Cats and Puberty

I left the title open for general discussion, but I do have a specific question.
My older cat, who is already spayed, hit her puberty at about 6-7 months (by which I mean she started going in heat) which I understood was the common time.
But my male cat, who is not yet neutered due to some circumstances, hasn't shown any signs of puberty (like spraying, aggressiveness..) even though he's over 1.5 years old! Is this normal for an indoor male cat, should I be worried or is it just a strange case?

At1.5 years old, there must be something odd with your cat. We mostly adopt male kittens and we have observed that before they even hit their 1st birthday, they already show signs of puberty. I do not claim to be an expert on these matters, just sharing my observation for the past 5 years of going back to cat owning. Consulting the vet should be the best option here.

I didn't think cats were supposed to still go into heat after they have been fixed. Am I missing something here?

My friends cat goes into heat too and he was fixed. Mine don't seem to do that, but they are both female and fixed. I did hear that sometimes they mess up the procedure and don't completely remove everything and they still continue to go into heat.

What are the problems of them not going through puberty?