IIRC if a player is an international (not in the CHL) then they can come over as early as 18yrs old and play in the AHL. Here is what the age eligability says on AHL.com
In the case of Larsson, he was drafted out of the SEL and has no ties to the CHL. It's because of this that he is able to be sent down to play in the AHL although he's only 19.What is the minimum age for an AHL player?
Per AHL By-Laws, the age limit for eligibility to compete in the American Hockey League is 18 years or over, on or before September 15 of each season of competition.