Adolescents are simply
those people who haven't as yet chosen between childhood and
adulthood.
For as long as anyone tries to hold on to the
advantages of childhood - the freedom from responsibility,
principally - while seeking to lay claim to the best parts of
adulthood, such as independence, he is an adolescent.
[...]
Eventually most people choose to be adults, or are forced
into it. A very few retreat into childhood and never leave it
again.
A large number remain adolescents for life.
(Gene
Wolfe)