Layer feed with a minimum of 16% protein is fine as a staple diet for Guineas that age. I'd cut back on the scratch you give them tho, it's basically junk food and lowers their dietary protein down too much, and IMO should only be fed in small amounts as a treat only.
I always provide oyster shell free choice to my flocks once they are 12-14 wks old (which is also when I switch them over to a layer feed), before the Hens start laying. Guinea eggs produce incredibly thick shelled eggs, and the Hens DO need the supplemental calcium or they will have to pull it from their body and bones... which will eventually take it's toll on the Hens, decreasing their productivity and it also increase the chances of other issues developing with their egg laying. Lack of calcium in their diet increases the possibility that they can break a thin shelled egg as they try to lay it and end up with egg yolk peritonitis, which is often fatal. Plenty of calcium also helps reduce the chances of a Hen becoming egg bound.
An ounce of prevention is worth a pound of cure.
~150+Guineas/6Flocks(18 Different Colors, plus assorted Pieds),3IB Peahens,1IB Peacock(HONK!),
51Turkeys(2WildX,2Mottled BlackX,2NarriX&45Poults),24Coturnix&1Button Quail,
16Silkies(POOFBALLS!),5 1/2Horses(The 1/2's a Mini),1BLM Burro(Livestock Guardian),9MuttGoats(Brushers),
2Rotts,3Red Heelers(On Guard),7Lazy Cats(Worthless),4FishTanks~
~150+Guineas/6Flocks(18 Different Colors, plus assorted Pieds),3IB Peahens,1IB Peacock(HONK!),
51Turkeys(2WildX,2Mottled BlackX,2NarriX&45Poults),24Coturnix&1Button Quail,
16Silkies(POOFBALLS!),5 1/2Horses(The 1/2's a Mini),1BLM Burro(Livestock Guardian),9MuttGoats(Brushers),
2Rotts,3Red Heelers(On Guard),7Lazy Cats(Worthless),4FishTanks~













