Penetrating the back of the paper is not the size of the wrist, but it means that when you look at it, people feel that the lines are "strong", not too "demon" and not too "hard" (my personal understanding is not too curved or too straight, not too thin or too thick, plus the ink is not too deep or too shallow), and the strokes should not be scribbled (written in the middle), and the pen should be strong and imposing (this)
As for the "thickness, there will be a three-dimensional sense", it is purely the general feeling of line structure, ink pen, paper and ink, depending on personal understanding. For me, it's proficiency and pen speed ... Look at the regular script of Yan Ti and Liu Ti, the official script of B X (Ying) tablet, and the seal script of Wu Rangzhi.
How long will it take to practice? Not necessarily ... it depends on copybooks, tools, teachers, individuals (interest, time, frequency, personal talent), constant pondering, appreciation and frequent asking. Ideal and ideal ... single digits (year! ) ... but people seem unlikely to be so perfect and grow up with the passage of time.
Whose handwriting is this? This is not my type of study ... very powerful ... evaluation ... I can't help you.