I have been in love with my classmates for 30 years. Is dreaming of a pure teenager an antithesis?

If it's wider, it's ok. Because the large structure is a predicate-object phrase without subject, the predicates "love system" and "dream back" are both positive in form, which is very good. There is something wrong with the small structure of the object part: Thirty Years of Classmates is a supplementary type: thirty years of classmates; Innocent Youth is a partial structure: innocent youth. I understand that your "30 years of classmates" refers to 30 years of classmates, which should also be partial structure, but the structure changes after the word order changes. The core of poetry antithesis is structure. If the structure is correct, the nature of individual words can be wider. As for leveling, it is good to conform to the rules.