In addition to the conditions mentioned in can. 656, nn. 3, 4, and 5 and others imposed by proper law, the following are required for the validity of perpetual profession: 1/ the completion of at least twenty-one years of age; 2/ previous temporary profession of at least three years, without prejudice to the prescript of can. 657, §3. Art. 4.
Source: Code of Canon Law (Vatican.va)