When we first got our bunk bed, my boys were 5 and 7.
So, only the older one can sleep on top.
They keep it this way since then.
My younger one never bother to sleep on top.
I have a friend, she only have 1 boy, he still has a bunk bed for himself
and sleep over.
So, it is upto you.
We will let our boys to stay in one room as long as possible,
We have another full size bed at guest room.
And, I don't care a few years later.
Our bunkbed is from Costco, for $1000.