Rook does not say exactly when it was that his magic manifested, but from a story he tells during Spectral Soiree we know he was still magicless by age 6.
In Book 6 he uses magic to create barriers, to dress the prefect in Pomefiore’s dorm uniform and to fight CHARON.
He also uses back to open phantom cages in Tartarus. Both Vil and Rook himself say that he never misses his target.
Simulation-Rook uses fire magic during Book 6, and we might see the real Rook use fire magic for the first time during the Eternity Float event where he comes it with ocean water to create steam.
Also during the Eternity Float event Rook use water magic to spray others with water.
Much like the rest of the Night Raven College group Rook uses magic to create fireworks during Glorious Masquerade, and in Book 6 he creates an entire island of ice.
Twisted Wonderland Reference Note 