There is no need to change to a "Layer" feed, and some benefit (admittedly limited) to not, offset by (usually) slightly higher cost and the rare inconvenience of buying or refilling oyster shell (or similar calcium source) in a separate dish.
Longer spiel here.
If you do choose to switch to a Layer formulation, the most important date is not age of your birds but rather "point of Lay". Are they laying yet? If so, switch. Are they not laying yet, but most are showing indications they are about to? (typically, "squatting" behaviors, pronounced reddening of the comb, sometimes exploration/sitting in nesting boxes) If so, go ahead and switch.
Start of Lay is a strong suggestion, which varies by breed and individual w/i the breed. Daily light levels have influence too - though that isn't likely a factor here, assuming you are Northern Hemisphere. If your birds are Production Red Hybrids (unlikely as you hatched yourself, but certainly possible), you are probably about there. If they are Brahma, Wyandottes, or plenty of other breeds, you may have several more months to wait...