For many, immaturity is an ideal, not a defect.
Mason Cooley
Youth ages, immaturity is outgrown, ignorance can be educated, drunkenness sobered, but stupid lasts forever.
Aristophanes
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one
Wilhelm Stekel
Immaturity is the incapacity to use one's intelligence without the guidance of another.
Immanuel Kant
Humanity has advanced, when it has advanced, not because it has been sober, responsible, and cautious, but because it has been playful, rebellious, and immature.
Tom Robbins
You can only be young once. But you can always be immature.
Dave Barry
It is the highest creatures who take the longest to mature, and are the most helpless during their immaturity.
George Bernard Shaw