Until a month ago all 3 of my kids shared a room. They are currently 7, just turned 4, and 19 months. ODD was 3 1/2 when DS was born and he slept in our room until 5 months old and then moved to the room with ODD so she would have just turned 4. Then when YDD was born she roomed with us until 8 months and then joined the older 2 in the kids room so they were 6, newly 3 and 8 months. They did fine.
Now we have 3 bedrooms so the 2 girls share. Ages 7yo and 19 months and 4 yo son has his own room.