Different Ages for U/M on different Airlines!?!

I just learned this one the hard way - everyone else may already know this, but here goes:

I used United miles to book a flight for my 14 year old daughter to fly to Montreal to visit relatives. Routing ONT - PHX - ORD - YUL. United's U/M policy is 12 and under, and she really wanted to go on her own.

Here's the snag - the first leg of the flight was on US Airways, and their U/M Policy is 14 and under! No mention of this on the United website, no mention when I booked, no mention when I entered her passport and NEXUS information (including her BIRTHDATE), and no mention when I checked in online.

So Mrs. chinookllc takes her to the airport, she shoos Mom away, goes through security, and waits at the gate. No problem, until she goes to board the aircraft, when they tell her she can't. OOOPS!

Long story short, she ended up on a different (ALL UNITED) routing and made it to Montreal this morning. One interesting part was when the US Airways Gate Agent spoke to Mrs. chinookllc and said, "...14 is the Policy and there's no way we'd go around Policy, well, until the end of the month when American buys us, because American's Policy is 12..."

Everybody else already knew about this, I'm sure, but just in case... be warned, the booking website doesn't always catch minor issues like this one...

Thank God the US Airways leg wasn't the middle one!