I would agree with everyone here - we recently (about 3 months ago) got a young female to keep our (then) 18 month old boy Riley. However, we wanted a cat that would be a bit younger than him, so he could show them the ropes and be the boss, but not a very young kitten, which we felt neither we, nor Riley, would be able to cope with!
![Evil Laugh :evillaugh:](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/evillaugh.gif)
We ended up getting Skye, a 4 1/2 month old female, but we took her on a 3-week trial basis (with the agreement of the resuce place), just in case things didn't go well.
It took a while, but with patience and making a big fuss of our big lad, it all went very well, and just 3 months on they are practically inseprable. She's active enough to keep him on his toes, but relaxed and grown up enough not to drive him to distraction
![Evil Laugh :evillaugh:](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/evillaugh.gif)
Good luck whatever you decide - but take your time making your decision, and choosing the new cat. Also, there are great tips in the behaviour guide section about introducing cats (as I'm sure you know!).