What is the ruling on falsifying the birth date of one's fiancée to bypass the legal age requirement for marriage in the country of residence?

There is no Sharia-mandated age for marriage. It is permissible for a girl to be married even if she has not reached puberty, provided that she is not handed over to her husband unless she is capable of intercourse. If she is an adult, her marriage is undoubtedly permissible. Falsifying age in official documents falls under forbidden lying, unless it is necessary to achieve a prevailing benefit and does not result in harm.