What is the legal age to run a site?

[ZiNgA BuRgA]

Contracts don't need to be signed.  At least in Australia (which should have similar laws to that of the US), the statutory definition of a contract is an agreement - it does not have to be in writing.  Written and signed contracts are just easier to prove in a court of law, than, say, verbal contracts, but as far as the legal system is confirmed, buying a product from a store is a contract just like signing an employment contract.  A defence against enforcing a contract, can be that one of the parties are unable to fully understand the contract, etc, but being a minor does not exempt you from enforcement.

Anyway, if the people said they weren't minors, would you agree to do business with them?