Looks like you have one of those gars that will taste test everything.. even if it cant eat it, the damage from the taste testing will usually result in severe injuries or death to the intended prey. And from my experience, you can have a pretty good idea how big a particular alligator gar will grow to from looking at their snout/nose. The longer the snout the faster and bigger it will get. The ones with the shorter snouts seem to max out at a smaller size.
According to my theory, the one you posted will get to 3ft fairly quickly (since it has a shorter snout) and then it will slow down. Meaning it will max out smaller than the average gator gar.