No idea, there was never a concrete number given for any of them.



All we know for sure is that they were at least 3 years old by the start of Re;Birth2, since they remembered Blanc, and at least 6 years old by the start of Re;Birth3 since it started after a 3 years time skip. So they would be at least 6 years old by the time of Re;Birth3.



Considering Nepgear wasn't even aware there were other CPU Candidates, they might have been born only shortly before the CPU's vanished.