erm well im still a minor (Only 14 sadly) but me and some friends want to open a stand next year in the venders area. i know that the 2008 con will be in portland again (thankfully for me since i live in oregon and i hate tax's on items. >.>) and i know the law here is before signing a contract binding you to something (in this case a table to sell some things at) requires parentel permision and stuff like that.
but does the con have any spicific rules about it? and do you have to be at the stand during full hours of the con or could you switch off with your friends who are running the stand with you?
Are you trying to have an artist table or a vendor who has large stock of product? There is no law of someone who is selling something at what age. A kid I know who was in grade school, his parents bought him candy wholesale to sell in this tiny store they built in their home and he'd sell it. But being 15 by next year and trying to manage a business and a booth is a lot of responsibility. Either way, even with parental consent, your parents would have to be at the booth with you. It's also illegal to make a contract with any minor and must be 18 or over to have a legal binding contract. You should understand that even if you have parental permission and the con decides that is OKAY, anything that you might do wrong is the responsibility of your parent and they can be held responsible to the fullest extent of the law.
As far as switching places on occasion, it's known that some people get a booth together so someone can watch the product and the other person can go to a panel or the bathroom, food run etc.
Be sure to read all the policies that pertain to what you're interested in and you'll get a clearer picture of what you're asking. You should also check the laws of your state.
g'luck