I would take Bock's advice. DEFINITELY read that article. Even if your cats have been around each other already... I've never given my cats anything to calm them down, but it's a personal opinion. I feel like that kind of thing is temporary at best and masks the problem instead of fixing it...
When I got my new kitten, I kind of just put the poor thing in the middle of the room and let them sort it out the first few days... Not really good advice.
What my ex and I did after realizing our mistake was let our older cats each have their own room (the bedroom for one and the computer room for the other) and kept the kitten out of those rooms for a few days. This gave the older cats a place to get away from her and have some peace. Even if you don't have the space to give each cat their own room, just having a secluded space for your boy to get away from the kitten should be okay. I would recommend giving your boy a way to hide up high a bit so that he doesn't have to be on the same level as the kitten. Don't force him to be around the kitten if he doesn't want to.
A lot of problems seemed to stem, too, from how hyper the kitten was. Both my older cats were calm and this new kitten was a hell-raiser. Even a calm kitten has more hyperactivity than an older cat. We found that we had to keep an eye out and if the kitten was too playful, we would seperate them and play with her until she was tired and then let them together again. Usually made for happier cats.
Our cats eventually got along quite well after some time (I think it was a few months) and will even sleep together and groom each other now. It did take time, though.
Another mistake I think people make is trying to get the stressed cat to be cuddly again right away. Give him space, let him come to you... If he wants picked up and cuddled, then by all means, do so. If he wants down, don't try to hold him to you. It will just make it worse. I would just let him do his own thing for a bit. He should hopefully come around in time.
Good luck to you and your cats. I hope they start getting along.