depends on a lot of factors...space, water changes/quality, feeding, temperature...but any gar species can easily reach 12" in its first growing season (not necessarily the same as first year in constant conditions of captivity), and Atractosteus genus fish can reach 15"+ in their first year under the right conditions.
will be interesting to see how they all do, especially since no one knows the secrets of how they raise the fish in Cuba before they go to distributors (those early life conditions play a very important role for growth later in the season/year/juvenile years).--
--solomon