You may want to consider taking a boat out BEFORE dinner. The last boat goes out at 4:45, and at that time you don't have use of both lakes (Bay Lake by the Lodge and Seven Seas Lagoon by the Magic Kingdom). You may be able to cross the bridge over to Seven Seas Lagoon, but expect to spend most of your time confined to Bay Lake. However, if you go out earlier you will be able to access both lakes.
To drive alone, you must have a valid drivers' license. 12 year olds can drive, provided they are 5 feet tall and are accompanied by someone with a valid driver's license. All you need is your room key (or a credit card), and driver's license. You do not have to be staying at that particular resort, or even a Disney resort to rent the boats.