Simplify the following text for a Grade 8 native English-speaking person.
Original: By 1472 , at the age of twenty , Leonardo qualified as a master in the Guild of St Luke , the guild of artists and doctors of medicine , but even after his father set him up in his own workshop , his attachment to Verrocchio was such that he continued to collaborate with him .
Simplified: In about 1472 , when he was twenty , Leonardo joined the Guild of St Luke , an organization of artists and doctors of medicine . Even after his father set him up in his own workshop , Leonardo still enjoyed working at Verrocchio 's workshop .