non-adult
/nɒnˈadʌlt/ /ˌnɒnəˈdʌlt/noun
A person who is not an adult.
adjective
That is not fully developed; that is not an adult; that is not intended for adults.
Origin
Late 18th century; earliest use found in John Hawkins (1719–1789), music scholar and lawyer. From non- + adult.