US law has some requirements on accounts created by minors which essentially means you must check the age for people creating new accounts, and you must not allow accounts for people < X years (but are not allowed to tell them up front).

I don't entirely understand where exactly this applies, i.e. why you can create accounts on some sites without giving your age. It might only apply in some telecommunication accounts cases, or maybe (possibly more likely), Google is one of the few companies subject to scrutiny here, so everyone else just flies under the radar.