Just brought home a new baby brother for my 3.5 year old adopted at 10 months cat, Autumn. I wanted to give her a sibling she can play with. I got both cats from the same adoption shelter. Autumn is very hesitant and hisses at Dewey but seems pretty tolerant already with this photo taken only a few hours after bringing him home. Dewey got up there all by himself and very much wants to play with Autumn. With some more time and introduction therapy I have a feeling she'll come around pretty quickly.
Read up on Jackson Galaxy's guide to cat introductions. I foster and have 2 cats of my own, so I go through the process a few times per year, and I still pull up his guide every time as a refresher.
Secondly, if you have an adult cat at home and want to adopt another, most cat experts recommend either a single adult cat or a pair of kittens, never a single kitten. Kittens are bursting with playful energy, and even a playful adult cat is unlikely to want to play as much as a kitten. When you have a pair of kittens, they can play with each other, while a single kitten is more likely to be annoying to your adult cat.