I am not positive about Pennsylvania, but most states only require license/ registration/ insurance on gasoline or electric assist bicycles if you exceed 50cc of displacement or exceed 20MPH.
I've got a 15 year old cousin who saved up for a few months and got one of these: http://spookytoothcycles.com/component/virtuemart/?page=shop.browse&category_id=6
I've got a 15 year old cousin who saved up for a few months and got one of these: http://spookytoothcycles.com/component/virtuemart/?page=shop.browse&category_id=6