Possibly last part because I'm almost finished the book)
[...] Momotarō [...] For all his closeness to his parents [...] could not identify with them; he found something unsatisfactory about the parents who had raised him. When he grew up, however he discovered a goal in life - the conquest of Demon Island - toward which he could direct the feelings he could not direct toward his parents, and thanks to which he was transformed into an adult [...] For him, the conquest of the demons was a kind of initiation into adulthood.
First of all "Momo"! It would be awesome if Berryz's Momo were to confuse me sexually & play this part in a TV series like Monkey Magic!
O.K. D. Khan link is simply that he was a conqueror too.
Also Demon Island reminds me somewhat of helloisland.com who upon 1st encounter with I tended to bash on the regular. So much so that I was afforded the title "H!I No.1 Pedo" for my efforts. Well I suppose you could say I was transfering some kind of inner personal conflict (demons) and I more or less changed my tune after a while.
Dr Doi is saying young people are like Momotarō looking to test their strength (but also that they risk becoming like demons themselves).