How we cite our quotes: (Book.Chapter.Paragraph)
Quote #4
His youth seemed never so vanished as now in the contrast between the utter loneliness of this visit and that riotous, joyful party of four years before. (2.1.34)
Amory can only think about the parties of his youth now that he's grown into a young adult. The shift saddens him, although let's be honest; it's not like he was the happiest kid in the world.
Quote #5
Tireless passion, fierce jealousy, longing to possess and crush—these alone were left of all his love for Rosalind; these remained to him as payment for the loss of his youth. (2.1.35)
After Amory has had his first true love with Rosalind, all that's left is his desire to destroy things and feel jealous of Rosalind's new lover. It doesn't seem as if adult life has left him with any positive emotions.