Dear Opinionated,
We are still waiting for Libby to get back with the data. I doubt their sincerity until then. So, all we have is an educated guess at a mathematical anomaly. If there really is one, (i. e. There are so much more twenty five year old girls available than twenty five year old boys.) there should be multiple solutions available. In the study of graphs, [as is the case with most mathematics] one number can not be changed, to achieve a solution. Changes have to happen in pairs. If there is a need for boys to marry younger, all the post high school boys that are employed, are the most eligible to fill such a need. Who has a harder time finding a shidduch; twenty one year old girl, looking for a learner or, twenty one year old working boy? Another question, how many twenty year olds, remain in yeshiva just for shidduchim?
Now, to your point. Assuming that there would be a need for bochurim to marry younger. One must stop his learning to perform a specific chessed. But learning precedes the acquiring middos. They follow naturally from responsibility and dedication, as people age. Also, Torah brings one to all these middos, as was discussed on some other thread. The learning of an independent mind, (One that is free is of external fashions and pressures.) is paramount and is not duplicated anywhere else in society. Not even computers. (At least so far.)