So many people overreacting here. Do what's right for your family. You'll know it's time when its time. Don't let others dictate that for you.
My son is 12 months and 18 days older than my daughter...I remember having the same worries based on others' reactions. But, I also remember a lot of advice that I would know when it is time. I can clearly agree with that because they stopped taking baths together at some point, but I can't even really remember when that was...though, seems like it was 6 & 7ish or so...like 1st and 2nd grade maybe? Honestly, I don't remember, but it happened and it all was fine. So, don't stress about it. You're not doing anything wrong!!
Mine are 16 and 15 years old now. And, they're completely well adjusted.
When we travel (it's just the 3 of us), generally, my daughter and I share a bed if sharing is necessary, but it's not unheard of that the 2 of them might share. We rotate sometimes...after all, I do pay for the vacation so I deserve my own bed for a night or two!
Mine may be teenagers, but I generally still get kicked sharing with either of them...and, yes, when we rotate, my son and I will share too. Nothing wrong with it! We are family!!! When they share, they generally line the bed down the middle with an extra blankets or pillows. I grew up sharing a bed with my older brother (by 4 years) when we traveled. It's normal! It's called being a family!
OP, seriously, don't worry about it and let other people's opinions bother you...you and your family will know when it's time to transition. It may be soon...it may be a few years. That's ok!