The ideal age to get guineas is as keets, actually. Most of the time, by 12 weeks, you can tell male from female, but by their calls more than anything else. The males most of the time have longer wattles and a more upright stance; they have a one-syllable staccato machinegun like call. Females sound like "Come back! come back!" or "Potrack! Pot rack!" Two syllables, however you interpret the sound of it. They can be vicious to chickens, though, at times. I had them and had to rehome them, long story. I miss the goonie-birds. They are unusual critters.