Welcome to BYC.
There are several options you can choose from for feeding your flock. If you want to feed layer ration you can switch them over at 18+ weeks and/or when they are laying - so, for your flock, anytime now. Alternatively, you can feed grower ration (as you are now) and offer free choice oyster shell for them to take in to meet their calcium needs for shelling/expelling eggs -- you can use this as a bridge until all of your birds have begun to lay, then switch to layer feed, or you can feed this way long-term. I, myself, use grower ration with oyster shell - I prefer the higher protein offered by grower vs. layer feed *and* I maintain a mixed flock where not all the birds are laying all the time, so it is a simpler approach than having to worry about who should/shouldn't have the high calcium layer feed at any given time (mixed flock is not just about gender, but also if you have females not laying due to age, molt, broodiness, etc)
