Aside from being wrong about blaming the so-called age-gap on the “shidduch crisis”, even if for arguments sake we assumed you were correct, there is no way to enforce a rule limiting future marriages to couples within “X years” of each other. If such a rule were proposed or implemented (or even encouraged), it would become a mockery and mostly disregarded. (See how little people follow the many calls of Rabbonim to limit the costs/lavishness of l’chaim/vorts and weddings — something that is easier to follow and even enforce.)
(This is in addition to your using bad data. In the past, Yidden generally married earlier than today, plus had a greater age gap than today. It was once not uncommon for older men to marry very young women.)