En fait elle avait 18 ans quand le prophète est mort, pas au moment de consommer le mariage
'A'isha (Allah be pleased with her) reported that Allah's Apostle (ﷺ) married her when she was seven years old, and he was taken to his house as a bride when she was nine, and her dolls were with her; and when he (the Holy Prophet) died she was eighteen years old.
https://sunnah.com/muslim:1422c