If the age gap is truly the issue and it is causing a disparity in there being more girls than boys looking for Shidduchim, as a number of Rabbonim and askonim are saying, then indeed repealing Cherem Rabbeinu Gershom’s prohibition of polygyny, something the Gedolim have a right to do (in fact R”G himself set an expiration date), would help the Shidduch Crisis.
Obviously, even when permitted, polygyny would be for a small minority of marriages and not for most.