Gosha, I have a 1 year old who was alone all day and I decided to get him a companion cat. At the time we had lots of ferals outside of our house and he'd pounce on the door to scare them and watch them scamper away, but he'd also twist over on his back and try to play with them through the glass door. One day we brought home a stray and after a day or two, we let them stray out of the bathroom to play with my 1 year Cuddles. At first Cuddles was sooo skittish. He's never been up close with another cat, and he scampered away and was scared. The stray was a super social 5-6 month old, and it was very obvious he wanted to play. However, when he saw how skittish Cuddles was, he backed down. After a day though, the two of them were wrrestling and playing (nicely most of the time). Eventually we gave the kitten away to get adopted and Cuddles was by himself again. After seeing him interact with the kitten, we decided he needed a companion.
Some people are suggesting getting an older cat who's already established a personality, but I disagree. When I wanted to pick my Cuddles a companion, we decided on a kitten because we thought Cuddles would like to play with him. I simply went to the shelter and observed the kittens. I basically picked the friendliest and most playful kitten there. He didn't bite, scratch, growl or hiss at anyone. He was eager to play and had a ton of kitten energy. We brought him home and at first HE (Simba) was scared of Cuddles. Cuddles was WAY over rambunctious and he outweighed the kitten 12 lbs to 3 lbs. The kitten would cry often when they wrestled and we had to break them up (I think Simba was just a whinny baby
Now Simba is around 5 months old and they get along great. Cuddles doesn't really play anymore with toys (at 1.5 years), but he DOES love to play tag with his new brother and he loved to stalk and pounce on him. They spend hours a day just chasing and pouncing on each other
I think getting him the kitten definitely made him "younger" (as another posted had noted). Simba follows his older brother around wherever he goes, and Cuddles watched Simba do crazy and naughty things (like last night when he got INTO the sofa and started scratching it from the inside..*Sigh*
Long and short: from my experience, get him a kitten who is friendly and social and they'll both be fine! Just be prepared to spend a lot of energy playing with the kitten, cuz holy cow, those little rascals never stop!