We have just taken our loft bed off Mr 16. He's had it for about a year and in the last few weeks of having it, commented that "it's hot up here".

Apart from that we've had no problems. It's a metal, king single one, very secure. (don't know the brand - we were given it) I often climbed up and had no feeling of it being rickety with it. We put DS2's bed underneath, firstly in a L shape to the top one, then when we needed more room, right in under like a bunk.

I think I'd be concerned with putting a 7 year old in a loft bed. Ours was certainly higher then a normal bunk, the bottom rung of the ladder was a lot higher then normal bunks as well.