A South Sudan immigrant and standout basketball player at a Catholic high school in Canada has been arrested after it was revealed that his true age is not 17, but closer to 29, the authorities said.

The student, Jonathan Nicola, who is 6 foot 9 and wears size 16 shoes, had been attending Catholic Central High School in Windsor, Ontario, as an 11th grader for the past six months after arriving on a student visa, The Windsor Star reported. He was so good that his coach was promoting him as a prospect to play in the N.B.A.

But the Canada Border Services Agency has accused Mr. Nicola of misrepresenting material facts on his application for a study permit. He was arrested after the authorities showed up at the principal’s office at the end of a school day this month and asked him how old he was. He admitted he wasn’t 17, immigration officials said.