This Side of Paradise is F. Scott Fitzgerald's first novel, published in 1920.
"The Dominating Intention" is an essay by Barry Gross, originally published in the textbook Novels for Students in 1969, and reproduced with permission on eNotes.com in the Study Guide section, under Criticism.
Since "The Dominating Intention" is itself a critical essay, it should only be used to inform a separated thesis statement. You should not simply copy the thesis from the essay, but you can support your own argument with properly attributed quotes from the essay to show how other scholars think.
One very good thesis statement for the novel would involve the protagonist's search for meaning in his life; Gross refers to this as "a deliberate and necessary search for an alternative." To elaborate, Gross thinks that Amory Blaine grows as a person, discovering the importance of "deliberately" seeking out new influences. Your thesis might then read: "The path to adulthood as exemplified by Amory Blaine is rooted in self-examination and the will to look for higher understanding." Although the topic is similar, the thesis itself is different, and you can use selected quotes from Gross's essay to prove your point.
Another good topic is the path from childhood to adulthood as affected by parents; early in the novel, Amory's mother describes him:
"This son of mine," he heard her tell a room full of awe-struck, admiring women one day, "is entirely sophisticated and quite charming -- but delicate -- we're all delicate; here, you know." Her hand was radiantly outlined against her beautiful bosom.
(Fitzgerald, This Side of Paradise, Google Books)
He is raised from birth with the notion that he is special and deserving of special things, but takes too little effort to achieve his own dreams, instead trying to live for others. Only at the end of the book does he realize that he has not worked hard enough to realize his own passions and desires. Your thesis here could be: "It takes Amory Blaine years and several rejections to understand that he must live and strive for himself and not others." This falls in line with Gross's own thesis, that Amory examines his worldview and discards it, and here as well you could use selected quotes to support your opinion.