If he's really a bully tadpole, he won't be getting arms and legs this year . . . . they usually take two seasons. But if he was that small when the boys got him, he's most likely NOT a bullfrog. Keep watching him . . . usually takes between 6 and 12 weeks for most of them to turn into frogs and if he starts to show little bitty backlegs at the base of his tail, he'll turn this season . . . .
Also, if he's a bullfrog, he needs protien . . . try smushing some pond snails and tossing those in with him . . .