Dating younger is NOT the main cause of divorce or shalom bayis issues, although it is definitely a contributing factor. When younger people go into a marriage with the wrong ideals, they often need assistance to be “brought down to reality”
But immaturity alone can be worked on more easily than other BIGGER matters that can break a marrriage. I know of many immature people that needed help but definitely were on their way to a strong marriage with the proper guidance. Obviously there are always exceptions (though these people tend to have more problems than just immaturity).
Perhaps immaturity has to be clearly defined.