Definition of "immature"

And thou also canst best account for the causes of her immature death […] .

1748, [Samuel Richardson], “Letter CDLXXXI”, in Clarissa. Or, The History of a Young Lady: […], volumes (please specify |volume=I to VII), London: […] S[amuel] Richardson; […]

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 - As quoted in The Catcher in the Rye (1951) by J. D. Salinger.

There are many genera and even families of Brachypylina for which immatures are not yet known, and thus numerous examples of adult convergence and misclassification remain to be revealed: such is the case with Hypozetes.

2001, DE Walter, H Proctor, RA Norton, Acarology: Proceedings of the 10th International Congress, page 51

While on a walk the next morning I found what looked like a patch of old growth habitat - perhaps somewhere the fires had missed - and to my astonishment saw a female Red-lored Whistler accompanied by an immature.

2005, Sean Dooley, The Big Twitch, Sydney: Allen and Unwin, page 240