I bought one of those hanging tent things (from Ikea) even before LO was born, but haven't put it up yet. I know it depends on personality, but just for fun:

At what age would your LO be to have one of those hanging up without having to worry about it being pulled down and having part of the roof fall down on them?

http://www.ikea.com/se/sv/catalog/products/20130878/