alt Hacker News> at the age of 13, Michelangelo was apprenticed to Ghirlandaio. The next year, his father persuaded Ghirlandaio to pay Michelangelo as an artist, which was rare for someone that young
He was literally getting education in art. It is not like there was no structure.
The apprenticeship was after this was painted. Prior to engaging in formal training he largely ignored school and spend his time painting and seeking out other painters to learn from:
> As a young boy, Michelangelo was sent to the city of Florence to study grammar under the Humanist Francesco da Urbino. Michelangelo showed no interest in his schooling, preferring to copy paintings from churches and seek the company of other painters. [0]
You can search other sources and you'll find the same: prior to apprenticeship he was not formally enrolled in any form of art education.
0. https://en.wikipedia.org/wiki/Michelangelo