I shared with my sister from when we were 3 and 1 until we were about 9 and 7. DH shared with his brother most of his life too.

We've both said we are not going to inflict room sharing on our children! And we're also aiming for us to have our own rooms in the next house (not bedrooms, but a reading room for me and DH's workshop). It can work well if siblings get on well and are friends, but I really hated having a little sister most of my life. We are friends now though!