Oh, I thought they all made them when they were mature. Mine was small (not marked as a baby though) when I bought him (I'd say he still isn't as big as the betta I had before though). I've been waiting for the flaring (which I know he can do as he flared at my finger in the shop and I bought him because of that and his liveliness but hasn't since then)... and not so much as a single bubble yet.
I should try and measure his body length later so I can estimate his age... there must be an approximate guide somewhere online.