Don't worry, it's not that strict and no one asks for ID to verify age. It's mostly based on the honor system and the "You can't be serious" test. I've never seen anyone who appears to be at least in their 50's have a problem. Similarly, the rule is supposed to be for babies and small children, but you will see many parents trying to hoist their 150-lb 12-year old into their arms when they want to get through immigration lines quickly. I have also never seen these people suffer anything more than a raised eyebrow.