Mine went into separate rooms at 12 months. I always felt that I wanted my baby in the same room as me for the first year, and that didn't change when I found out I was having twins. I never intended to co-sleep, but found that I was and I actually liked it.
We still co-sleep for part of the night, but they go to bed in their own separate rooms. They wake up sometime between 12 and 3 normally, and then they get up and wander in of their own accord.
Mine made the transition to separate rooms completely painlessly. I was really quite worried about how it would affect them, but they didn't even seem to notice. In fact, by DD, who'd been waking several times throughout the evening and night and needed resettling, suddenly started sleeping through when I separated them. My DS snores quite badly, so he was obviously disturbing her.
Needless to say, they are now 2 (this saturday ) and are still getting in bed with me at some point during the night.
I read somewhere that there are optimum ages to split twins, whether that's at school, sleeping arrangements, or whatever. Apparently, you need to do it while they're very young or wait til they're a fair bit older. That said, every child is different and what works for one set of twins might not work for another.
I'd say go for it. If it doesn't work out and they scream the place down, then they're obviously not ready for it and you can put them back together in the same room, no harm done.