Technically, a cardinal is a Papal advisor & elector, and can be a layman. Leo X became a cardinal at the age of 13, and Pope at the age of 37.
Pope Leo X was the first pope to kill a cardinal, and he killed his pet elephant by feeding him a laxative mixed with gold. He hired 10K soldiers to start the War of Urbino, dividing what should have been a united Christendom against the attacking Ottoman Empire but instead caused war in Europe between Christian nations from Feb 1517 to Sep 1517 (hint: one month before Luther's 95 Thesis in Oct 1517). Oh, and he charged people money (indulgences) to have a priest pray for your sins to be forgiven.
But other than that he was a good guy. LOL