Passage: By 1751 his success and his vanity had grown to such a point that he is reported to have said, "There are but three great men in Europe—the king of Prussia, Voltaire and I." He was an excellent mimic as well as dancer. From 1770 to 1776 he was a master and composer of ballets, retiring, in favour of Jean Georges Noverre, with a pension.Vestris married a dancer, Anna Heinel (1753–1808), of German origin, who had a wonderful success at the opera. He reappeared at the age of seventy-one on the occasion of his grandson's debut.

Question: what age was he when he appeared at his grandson's debut?
seventy-one