+...1? 2?....xD Either way, I agree. Hard to make a perfect estimate, but the smaller the betta generally the younger they are.
I've noticed Petsmart(or at least the one in my area)has been getting in some really young HMs, DTs, and females. Last I went in there all their HMs were absolutely preciously tiny! Couldn't have been more then 4 months old.
The VTs and CTs and PKs I see though look to be a good 6-9 months...some of them are even too large to move around much in their little cups! Its really quite sad...