So github.com is the violator, here, since it's a software application that may be run by a user on a computer and can download applications (loads of them!).
There's no further elaboration on what age signals are preferred, so my assumption is that a DoB field in the user profile and a system service to request the age bucket is good enough. It's absolutely silly, but DB48X could implement that.
There's a related question of who is actually liable under this law - it seems written to target just Apple, Google, and Microsoft; and it only makes sense in the context of consumer electronics. Like, how does this work with enterprise systems? Servers? Is IBM going to have to rush out a patch for z/VM to ask the system administrator what their date of birth is?
You put the age of the owning company. If the company is under 18 then too bad for you.