Really slugged through this one. G. Stanley Hall is not a bad writer, actually for a scientific treatment its written in an entertaining style and there are a few moments in the book that are genuinely interesting like his treatment on pedagogy or masturbation, but these parts are few and far between.
The remainder of the book treats other subjects like psychology and physiology but does so with an underlying theory of evolution that would be accepted by no one today. Such as the framing as each human developmental stage being an expression of some lost ancestor, racialism, or the framing as internal organs competing against one another, the critique of evolution being a projection of strife in the "survival of the fittest" onto the universe is taken to a ludicrous level and is latent throughout the entire work.
Personally I read this book because I have found multiple sources that refer to this work and G. Stanley Hall as the founder of the term, or concept, Of adolescence or teenage. I was hoping to find in the text, a reason why after thousands of years of civilization there was at that time a need to separate "man" and "boy" with the new category of Adolescence. I, Unfortunately found very little.
There is today a new category that is proposed by Jeffery Arnett, A man who is a professor at the same college that Stanley Hall taught at called, Emerging Adulthood. It describes a novel phenomena of young twenty somethings who are for a number of reasons, incapable of or unwilling to be a function independent adult. It is obvious to me, and likely to many why this is. College debt, mass migration and a higher competition for jobs, combined with the suppression of real wages and increased real estate cost leads to less young Adults that are able support themselves. To me it seems impossible that there was not some similar story about the coining of the term, or concept of Adolescence, but like I said I did not find any clues in the text.