It's not really about being immature. It's about having a lot to learn about a given area of life. Not all of us, however mature and sensible, are well-rounded.
The Page Pentacles indicates they need to give more attention to the physical world (everything from their physical health to their home environment to their income).
The Page Cups indicates they need to learn more about emotional response, or about how to read and deal with other people's emotions.
The Page Swords indicates they probably would benefit by the mental discipline of an academic course of study, or by regular reading, or by even online brain-training exercises.
The Page Wands indicates that they need to give more attention to what they *do*, how they use their energies (or even start a needed exercise programme!).
None of them say that the whole person is immature. All of them say they have something to learn in ONE area of their life.