Signing Age for Minor League Baseball

From Ask the Baseball Pro:
Ryan wrote:
How old can you start playing minor league baseball?

From the Baseball Pro:
If you are from outside the US you can sign at the age of 16. If you are in the US you must have a high school diploma. To my knowledge that is the earliest you can sign.
Your Baseball Pro, Steve Holm

P.S. As a parent, I wouldn’t want a high school player travelling with a professional baseball team. There are too many long days on the road, and an underage player shouldn’t be hanging out in bars. It’s best to get experience in high schools and colleges, particularly community colleges.
Team Mom, Jean