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1/ Yes for American kids. They draft from both high school and college. However, unlike the #nfl and #nba, these kids have 3-5 years in the minor leagues before they see the majors.

2/ Outside the US, there is what is called the international free agency market where the kids are signed at about 16 to contracts. Each team has a certain amount in bonus money it can spend and it has to spread it over its signings.

3/ Alvarez, the kid we just mentioned, is from VZ so he was an IFA signing as a 16 yr old. He is now in the majors at 21.