I have a 14 year neutered Huge black&white longhaired male cat.
He’s cranky one minute and purring the next.
I recently brought in two kittens - and he’s totally fascinated with them. Actually likes them.
Watches them play and has even started playing again himself.
So neat to watch.
I think you would be delighted with the results of bringing home a kitten. Especially, if you brought in two! 
In my experience:
Cats can become sexually mature as early as 4 or 5 months, though 6-9 is more common, if that is the definition you want to use to define a kitten.
They tend to stop growing somewhere between 12 to 18 months.
Their personalities are often more or less set by the time they are 9-12 months old.
Cats can be spayed or neutered as early as 2 months old, though many vets still wait until they are 6 months old. I think it’s largely a matter of preference (spaying is tricky surgery, apparently!).
Whatever Zsofia got, it’s 5 years older than that now!
And they may even settle it in a way that’s logically inconsistent. Two of the cats who lived with my mom managed to reach a mutually-agreeable arrangement where the youngest was dominant over the oldest by virtue of the oldest being the youngest’s daughter, while the oldest was still the dominant mammal in the house by every standard. No, it didn’t make sense, but somehow, it worked.
Hey, I did say that it didn’t make any sense, didn’t I? But that’s what they settled on. I guess it might have something to do with the young cat being larger than the old one, and she got pregnant very young, and maybe decided that that meant that she must therefore be a mommy.
So how’d it work out, Zsofia?
I got a kitten who entirely disrupted poor Dewey’s day. I was in tears for weeks because I thought I’d completely ruined his life until I came home one day and found them curled up in a basket together. He’s quite a bit bigger now. (Dewey is the tabby, Edison is the “kitten” in question, the huge fat orange one, and the black one is Stokie who was a “free” feral cat I nabbed from under a porch with the intention of finding him a good home because he seemed quite attracted to humans. I did, indeed, find him a good home, unfortunately.)
I can’t believe Edison must be five years old now! That’s just crazy!
nm