A CRBA can be requested up to the time the child is 18, but I think that makes the request one that has to come from the parent as well, because the child hasn't reached the age of majority.
The State Department also offers that a passport can serve in lieu of a CRBA, but passports expire and CRBA's don't expire. Particular advice from a Consulate Officer is mixed, some insist on a FS-240 to get a passport, others don't. As a matter of law, either an unexpired passport or a CRBA is conclusive (outside of court) as to citizenship.
Now, back to birther battles!
My daughter is long past 18, and does have a US Passport, but to get it she had to submit her Canadian birth cert, and her Certificate of Naturalization.
I really hope that Cruz’ parents submitted the proper paperwork to make him a citizen from birth. We never even thought about it, and it was only the debate about Cruz that made me think of it just this morning.