What is the ruling on someone who wishes to marry a girl 12 years his junior? Is it permissible for him to send her a gift through a female relative to congratulate her on her success? And is it permissible to delay the marriage on the pretext of the girl completing her education?

There is no objection to marrying someone younger than the mentioned age, and completing education is not an excuse to delay marriage; rather, both can be combined. Offering a gift to the one whose marriage is desired is permissible because it is a cause for affection and acceptance. However, it must be noted that this woman, before the marriage contract, is a stranger (non-mahram), and private seclusion with her is not permissible.