FWIW... Dominicans can sign at 16 years old and many of the best ones do sign at 16. Actually I believe they can still be 15 if their 16th birthday is within 45 days of the July deadline.
BTW, we had a Cuban pitcher in Jupiter this year, his name was Sierra. The Dodgers just signed him for somewhere around $35 million today. Forget how old he is, but he wasn't very young.