Hmmm... 7, eh. Not sure. When they first told me about the restrictions, they commented that "it's a really long walk, up stairs -- we advise elderly and kids not to do this." They didn't really say they COULDN'T go -- but the desk CM made it certainly clear our 2 yr old shouldn't go due to safety reasons.
Personally, I found the "arduous climb" they warned me of to be no biggie AT ALL. (I think the CMs often forget how much walking we tourists have already done -- a few stairs is a piece o cake!) Could my then-7 yr old have made it? Absolutely and more spryly than I, you can bank on it. I imagine however they will want your assurance that he will listen to the adults and not get reckless up on the roof. A family with several kids in tow would probably pose more of a problem. (We have three and on that trip, they were ages 7,6, and 2... a three ring circus suited more for the Big Top than a roof top!) And we just didn't think we could take one and not another.
So did I hear express limits on ages? No. If anyone else did hear of such a limit, feel free to comment. But they made it clear that our party had to be "capable (of the climb) and in control".