Hi!
Buying a snake from a local pet store (especially commercial ones like Petco/Petsmart) comes with downfalls. Not a lot of stores keep specific records of their animals, especially reptiles, when it comes to age, birth/hatch date, weight, etc. So you will have to guess on some parts. That being said, a lot of snakes in stores are wholesaled from breeders. This looks like a hatchling, no more than a couple months I would say. But I can't really see the entirety of the animal, if you can take full body (stretched out if possible) or a size reference photo I'm sure I, or a more experienced keeper can give you a more accurate guess.
As far as the waterbowl thing goes. What is the temperature and humidity in the cage? It may be too hot or not humid enough.