My kids shared a room when they were about those ages and they still share a room. As the other commenters said, I think it's good for kids to share (my two are both boys, so they share not only a room but all the same toys). The only problem I had was that my younger son would tend to take 2 naps a day while my older son still took one, so they "tag-teamed" me with naps most of the time. Although he wasn't quite ready for it, I more or less had to force my younger son to give up his two shorter naps and move to taking one long nap so that both kids would be napping at the same time. Otherwise, I would spend something like nearly 6 hours of every day trying to keep one child quiet while the other one slept (in their shared room which had most of the toys, naturally), and I got almost nothing done every day and was quite frazzled.
Oh, and my younger son was not sleeping through the night at the time, but he rarely woke up my older son. I guess he just learned to sleep through it, or was so heavy a sleeper that it didn't disturb him.