If I already have a cat (or a kitten), and I want to get another to keep it company.
Say the cat I have already is a couple years old, is it okay for me to get a new kitten? Or the other way around? it matter what age the new cat is?
A few general observations from my experience:
I have integrated new cats with cats from all ages from a few years to 15 years. All went without serious incident. When adding a kitten to a really old cat there can be a bit of friction if the kitten does too much roughhousing, but this is fairly easily dealt with.
If the difference is only a few years, then the older can probably handle kitten energy and will feel less threatened by a small newcomer. The pecking order settles in fairly naturally.
I'm unsure if age deltas make a big difference.
I feel a young cat is more likely to accept another cat than an old cat (but am not sure on this), but the biggest factor is how the personalities an insecurities work with each other.
I've had at most 4 cats at one time. The first two cats adjusted relatively easily I think because of their temperaments and they were relatively young (less than 3 yrs old). The next two cats I got when everyone was older and the adjustment wasn't as good.
Cat #3 wanted to frighten cats 1 & 2 into leaving the house. Cat 1 figured out 3 was a paper tiger and would call bluffs, cat 2 was always scarred of 3. Cat 4 is loopy and fun loving, but as a result of 3, 2 takes 4 too seriously, 1 is just kind of leery of 4 but not really bothered. So I think the biggest factor was the personalities involved.
It depends on the person who adopts a cat.
From my experience:
I've got 2 cats. The first one I got when she was 4 weeks. She was small and cute. Everyone likes kittens :). And I managed to educate her, breed her how I want. However, I didn't know whether I would be successful or not (as with children, we can never be sure no matter how hard we try). Some people say it's better to adopt a kitten as in this situation the kitten can get used to the new family much easier. But they need more attention. Kittens play, play and play. They have so much energy, so they sometimes ruin your stuff, just because they are bored. They need to be played with a lot.
In 2 years I adopted an adult cat. She was grown up, about 6 years, and it took about 2 weeks to get her used to our home, our house, and about 3 months to get her used to our rules (not eating flowers, not sleeping on the dinner table, not scratching our armchairs, etc). However, she perfectly knew where to pee. I had to buy special forage for her, new scratching mat, as she didn't want to use the existing scratching post. What is important: before adopting I knew her character, her personality, I knew what she likes and what she doesn't, about her habits, what fur she has, etc. Adult cats are more calm. They have less energy in comparison with kittens.
And this concerns all types of pets: bunnies, dogs, parrots. The choice between a kitten or and adult cat depends on what you want and what you are ready for.