Antonyms of adj schoolboyish

1 sense of schoolboyish

Sense 1
boyish, boylike, schoolboyish -- (befitting or characteristic of a young boy; "a boyish grin"; "schoolboyish pranks")

INDIRECT (VIA young) -> old -- ((used especially of persons) having lived for a relatively long time or attained a specific age; "his mother is very old"; "a ripe old age"; "how old are you?")

Similarity of adj schoolboyish

1 sense of schoolboyish

Sense 1
boyish, boylike, schoolboyish -- (befitting or characteristic of a young boy; "a boyish grin"; "schoolboyish pranks")
       => young (vs. old), immature -- ((used of living things especially persons) in an early period of life or development or growth; "young people")