This is a difficult question to answer. It's hard to operationally differentiate what is meant by "maturity" and immaturity.
A mature person is able to keep long-term obligations, is unshaken by flattery or criticism, holds a spirit of humility, their decisions are based on character such as values and principles, but not feeling, they express gratitude reliably, they know how to prioritize others before themselves by considering the needs of others and they seek wisdom before acting where immature person is deficient in maturity; lacking wisdom, insight, emotional stability, etc
Where maturity is an earned status that often carries responsibilities, immaturity is then defined in contrast by the absence of serious responsibility and in its place is the freedom for unmitigated growth.
An mature man always:
think more and more of others.
takes responsibilities.
fill mind with knowledge and use it more intelligently.
give more than you take.
An immature man always:
Thinks of the present and never about the past or the future.
Can't express his/her feelings in a positive way.
Puts wants before everyone. Also doesn't discriminate between wants and needs.
doesn't act his/her age and/or isn't responsible.