I have an almost 5 y/o - and we still sleep in the same bed. Neither of us sleep that great when we are in separate beds anymore. My philosophy is: as with breastfeeding, the child should lead the way. Children will definitely start showing signs of desired privacy and independence around 6 years old - and that is when I feel giving them their own room and bed is more appropriate.
We must not fail to realize these are our CHILDREN, these are not miniature adults. Children are FORCED to do so many things that older children should be doing... and our society wonders why kids are turning to violence, sex, drugs/alcohol, etc at such young ages - - because our society condones pushing them too far too early and they snap.
^ This is actually not directly pointed at you, but a general 'you' in our American society.