Petsmart and Petco are leaders in the field of mass animal abuse.
Their staff are not trained enough for all the different kinds of animals they care for, or to give proper instructions for each. They don't care enough to get their animals from ethical breeders.
These corporations view animals as inanimate commodities, and their only priority is getting as much income as possible regardless of the animals health.
To answer your question though I read somewhere that BP hatchlings are between 10 and 17 inches, so you can make a vague estimate from there. A few months old probably.
Sorry I don't mean to go off on a tangent on your thread.