The boy went into the bank last week brandishing a fake gun and shouted "Hold-up!".
Frightened staff handed over some money to him before the teen made his getaway.
The boy then raced off on his bicycle, and was chased by a witness in a car, 'RTE News' reported.
The teen was arrested by police while trying to cross the border into Austria.
He admitted to robbing the bank using a toy gun.