Majorana was only 5 years old and was able to extract the square and cubic root from multi-digit numbers. His sister wrote: "He must have been six years old when on the quay of the port he was able to calculate to a hundredth how much coal a certain ship had to burn to make a certain route".
I, on the other hand, feel so stupid... I read and reread these notes and I can't get over them. Maybe I should take a good refresher.