Four raws over about fifteen years, so let me give the honest version rather than the shop version.
Ages mine started: 9 months, 11 months, about 14 months, and one who has never said a word and is now seven.
What actually predicted it, looking back:
How it was raised mattered far more than age or sex. The two that talked earliest were hand-raised chicks that had been around human voices since before they could fly. The silent one was a wild-caught adult, and looking back, expecting a bird that spent its first years in a tree to start speaking Urdu was always optimistic.
Consistency beats volume. Two short sessions a day, same phrase, same tone, same time — morning while I make tea and evening. Ten minutes each. People shout a word at the bird forty times on a Sunday and then nothing for a week, and wonder why nothing happens.
Emotion is what they latch onto. Every one of mine learned things nobody was teaching: the doorbell, my mother calling my name, the sound the microwave makes. They pick up what the household reacts to, not what you sit and drill.
The bit I want people to hear. Do not buy a raw to get a talking bird. Most of the ones sold as "will definitely talk" are sold by someone who will not be there in eighteen months. Plenty never talk, and you are committing to a loud, extremely intelligent, thirty-year animal that needs hours out of the cage. If the talking is the point, you will resent the bird, and that is how they end up alone in a cage on a balcony for twenty years.
Mine is a good bird whether or not he says anything. That has to be enough before you buy one.