Definitions for underageˌʌn dərˈeɪdʒ
Random House Webster's College Dictionary
being below the legal or required age.
minor, nonaged, underage(adj)
not of legal age
dependent by virtue of youth
Kernerman English Learner's Dictionary
legally too young
underage drinkers; You can't come in if you are underage.
A deficit or shortfall in funds, inventory, or capacity.
below the normal or legal age for some activity, such as drinking or having sex
not yet a legal adult; still a minor.