I have 13 total chickens. 3 which are laying, 4 who are 18 weeks old and about to start laying, and 6 of whom i don't know their ages with the youngest being no younger than 12 weeks old. Im currently feeding them start and grow and know not to switch to layer feed once they all start laying. Question is would waiting another 6 weeks be too early to switch to layer feed or should i wait longer? Also if i put oyster shell supplement for the laying birds would the younger ones go for it as well?