When should opposite sex children stop sharing a room?

The anonymous question here, my children, 5yo (girl) 3yo (boy), have shared a room since the youngest was born. My 3yo (boy) has recently transitioned to a toddler bed and will transfer to my daughter’s bed some nights. We just bought a house, and we were excited for them to have their own rooms. But we decided to let them continue sharing a room until they were ready to have their own. I just thought it would be a lot of moving houses, then separating them. I was talking to my Mom about this, and she treated me like I was crazy, letting them bed share. I’m conflicted because that never crossed my mind that it was somehow inappropriate. Any advice?

No issues with this. They are siblings. and sleeping.