For a family in Europe the question is not really “at what age?” but “how do we start when he only hears Arabic from us?” The difference matters: a child in Cairo hears these sounds in the street; yours hears them only at home.
Before 4: listening, not teaching
No lessons, no letters. Ten minutes of recitation a day builds the ear and makes the sounds familiar before they are ever asked for. This stage is exactly what compensates for the absent Arabic-speaking environment.
Ages 4 to 6: letters as play
Ten to fifteen minutes, no more. At this age the measure of success is not how many letters are retained but whether the child still wants to come back. A child forced at five refuses at ten.
Ages 7 to 10: the ideal window
Pronunciation maturity, sharp memory and willingness to follow a routine all arrive together. Most adults who articulate the letters correctly began in these years. Two thirty-minute lessons a week and five minutes of daily review are entirely sufficient.
And after 12?
Nothing is lost. Teenagers grasp the rules faster, but pronunciation takes more effort because the mouth has settled into another language. The remedy is direct correction from a teacher, never silent repetition.
The weekend-school trap
Two hours a week in a group leaves each child only a few minutes of reading aloud. Socially valuable, technically insufficient. Two short one-to-one sessions a week achieve more — because the child speaks for half the time.