al-Haafith Ibn Hajar al-‘Asqalaanee said:

((I drank some (Zam Zam water) once, whilst I was (just) beginning my studies in hadeeth, and asked Allaah to bless me with the level/calibre of ath-Thahabee in memorising hadeeth. I then performed hajj after a period of about 20 years, and found myself to have exceeded that level/calibre. So I asked Allaah for more than that, and I hope that Allaah will grant me that))

al-Hifth – Ahammiyyatuhu, ‘Ajaa.ibuhu, Tareeqatuhu, Asbaabuhu – Page 65

Juz. fee Hadeeth ((maa.u Zam-Zam limaa shuriba lahu)) libni Hajar – Page 37

Ref: Fatwa-Online

Ibn Qudaamah al-Maqdisee said:

"After this, I advanced to school and memorised the Qur’aan when I was only six or seven years old. I would then fast all the time, my daily sustenance was bread made from barley and thereafter I would wake during the night in order to pray."

Ref: The Advice of the Salaf Regarding the Early Upbringing of the Child - 2