I do not think 14 is too young, but as someone already posted, it all depends on the child. If it's space that you need, an easy answer to this would be connecting rooms. There would not be a need to seal the two rooms off from one another, giving the child (or parent, whichever is the case) the space they desire while maintaining a level of control. Another option would be more of a suite-type room that has seperate sleeping quarters for the kids / parents.

Hope it all works out!

M