Don't wait years. That's all I can offer you. Bird was alone his whole life until a few months ago, as well as Mango was in her own home before I got her. Bird was a screecher, any reflective surface no matter how small or how faint/distorted his reflection was, he would scream and scream and scream until he or the object was moved away. I finally got Mango as a way that I believed would help him, as well as having the interest in getting another cockatiel in the house. I introduced them slowly, in different cages slowly moved closer and they were fine for awhile. Kept their distances a bit but they were getting along. But Bird is decidedly other-bird aggressive and recently has gotten very unfriendly with Mango being around, I've had to separate them. They were fine for a month or so until this past week when I had to interrupt him chasing her angrily around the bigger cage I have and actually am worried its been going on longer when I was at work. They're always out when I'm home so maybe its something that I just didn't witness. And I'm wondering if the blame is partially on me, jealously wise between the two of them, since they seemed to be okay for awhile.
Surprisingly, even though they can't be near each other anymore, Bird has stopped screaming and reflections aren't the huge ordeal they used to be, so I guess in a way, Mango being around has helped even if it wasn't in the way I thought. It messes up the cage plans I've had for my birds and while I have no regrets taking Mango in, it's turned out to be a bigger commitment than I thought in having to now maintain three separate cages.
Like Ollie mentioned, theres always a possibility they won't get along and it's something you have to prepare for when taking an additional bird in. It's something I didn't consider. But doing it at a younger age helps to greatly reduce the problems of your first bird seeing the newcomer as a threat to their domain rather than as a friend. Waiting until you personally are ready to take another bird in is always the very best option for both you, your bird and the bird you'd be bringing in. But it's something I tried with a negative outcome, so just be aware of what can possibly happen. On the flip side, I still firmly believe that any bird benefits from a feathered friend in a way that we as people just can't provide, even as their 'flock mate'. Good luck with your decision and I really hope it works out for you!

just something to keep in mind.