The Directive on family reunification lays down the conditions under which third country nationals who reside legally in the territory of a Member State may apply for, among others, their spouse and their children who are minors to join them. In order to ensure better integration and to prevent forced marriages, the Directive permits Member States to fix a minimum age for the purposes of the reunification of spouses, which may not be higher than 21. That minimum age must be reached by both the sponsor and his or her spouse before the latter may join the sponsor. The Directive does not, however, define the date by reference to which the national authorities must determine whether the minimum age condition is satisfied.