Both of my older children coslept with us until they were about 2 1/2 ish years old. I transitioned my son out by putting him down to sleep in the crib and moving him into my bed when he woke up the first time and as he slept longer and longer he ended up spending the night in the crib eventually, but didn't end up sleeping in there all night until he was about 2 1/2 and had his own big-boy-bed. Then he would come into our room in the morning when he woke up and snuggle for a while, often falling back to sleep. He's almost 8 now, and on the weekends, he still comes in for a quick snuggle when he wakes up (5-10 minutes or so) before getting up and wandering away to read or play or do something with his younger sister until 9, which is when we've told them they can wake us on weekends (unless they need us for something important.)
My daughter, who is turning 4 this weekend, was transitioned out more deliberately -- we set up a toddler bed in our room and started her sleeping in that, but she could climb in whenever she wanted. Then after she was sleeping happily in that, we moved her bed into her big brother's room and she slept on it there for a while, and is now thrilled beyond belief that she has the bottom bunk of a bunk bed with her brother.
My youngest is 3 1/2 months old, and is happily cosleeping, and probably will until he's about 2 1/2 when we will do this all over again. At that point, we'll probably have the great bedroom shuffle as everyone moves around and possibly gets their own rooms. Right now, I think that both my 7 year old and my 4 year old sleep better with someone else in the room, though they are both also accustomed to being alone in the room because my son spends half his time at his dad's house.