No. It wouldn't be late-onset, because by definition, ASD is present from birth or early childhood. True even if it does not meet diagnostic criteria. It's very common for diagnosis to occur in the early teens, when a child who could handle the social expectations in elementary school becomes more challenged in middle school. You're right, it can first come to clinical attention even in adulthood - but it was always there, just not noticed earlier.
_________________
A finger in every pie.