This Might be of some help to you I just went digging through my old Reptile laws and found these to links to the laws.
Penn requires a special permit for people to collect Timber Rattlesnakes. No age is asked for this permit but as you must have a fishing license as well to collect reptiles a 16 year old can obtain this permit and license, So it would stand to reason and logic the State allows for 16 year olds to posses venomous reptiles.
http://www.fish.state.pa.us/
I still wonder why you would allow a minor to take possesion of a venomous reptile and to use a credit card without and adult present though. However the above information may help you to not suffer anything more than a very valuable lesson learned NOT TO SELL TO MINORS.
Scott Bice