What is Quadriennium Utile?

Legal Definition
Scotch law. The four years of a minor between his age of twenty-one and twenty-five years, are so called.

2. During this period he is permitted to impeach contracts made against his interest previous to his arriving at the age of twenty-one years. Ersk. Prin. B. 1, t. 7, n. 19; 1 Bell's Com. 135, 5th ed.; Ersk. Inst. B. 1, t. 7, s. 35.
-- Bouviers Law Dictionary
Legal Definition
In Scotch law. The term of four years allowed to a minor, after his majority, in which he may by suit or action endeavor to annul any deed to his prejudice, granted during his minority. Bell.
-- Black's Law Dictionary