From BiblePortal Wikipedia

Vine's Expository Dictionary of OT Words [1]

Na‛ar ( נַעַר , Strong'S #5288), “youth; lad; young man.” This word is found in Ugaritic, and it seems that the Egyptian word na-arma —(“armed retainers”) is also related to the West Semitic usage. The root with the meaning of “youth” occurs only as a noun and occurs in Hebrew in the feminine ( na‛arah , “young girl”) as well as the masculine form (e.g., Gen. 24:14).

Na‛ar occurs 235 times in the Hebrew Old Testament. Its use is predominant in the Pentateuch and in the historical books. The first occurrence is in Gen. 14:23-24: “… I will not take any thing … save only that which the young men have eaten, and the portion of the men which went with me, Aner, Eshcol, and Mamre; let them take their portion.”

The basic meaning of na‛ar is “youth,” over against an older man. At times it may signify a very young child: “For before the child shall know to refuse the evil, and choose the good, the land that thou abhorrest shall be forsaken of both her kings” (Isa. 7:16). Generally na‛ar denotes a “young man” who is of marriageable age but is still a bachelor. We must keep in mind the opposition of youth and old age, so that we can better understand that Jeremiah, while claiming to be only a “youth,” was not necessarily a youngster. In truth, he argued that he did not have the experience of the older men, when he said: “Ah, Lord God! behold, I cannot speak: for I am a child” (Jer. 1:6).

Absalom was considered a na‛ar , even though he was old enough to lead the troups in rebellion against David: “And the king commanded Joab and Abishai and Ittai, saying, Deal gently for my sake with the young man, even with Absalom” (2 Sam. 18:5). A derived meaning of na‛ar is “servant.” Jonathan used a “servant” as armorbearer: “Now it came to pass upon a day, that Jonathan the son of Saul said unto the young man that bare his armor, Come, and let us go over to the Philistines’ garrison, that is on the other side” (1 Sam. 14:1). The na‛ar (“servant”) addressed his employer as “master”: “And when they were by Jebus, the day was far spent; and the servant said unto his master, Come, I pray thee, and let us turn into this city of the Jebusites, and lodge in it” (Judg. 19:11). Kings and officials had “servants” who were referred to by the title na‛ar. In this context the word is better translated as “attendant,” as in the case of the attendants of King Ahasuerus, who gave counsel to the king: “Then said the king’s servants [NASB, “attendants”] that ministered unto him, Let there be fair young virgins sought for the king” (Esth. 2:2). When a na‛ar is commissioned to carry messages, he is a “messenger.” Thus, we see that the meaning of the word na‛ar as “servant” does not denote a “slave” or a performer of low duties. He carried important documentswas trained in the art of warfare, and even gave counsel to the king.

Another noun no‛ar means “youth.” This noun appears only 4 times in the Bible, once in Ps. 88:15: “I am afflicted and ready to die from my youth up: while I suffer thy terrors I am distracted” (cf. Job 36:14).

The Septuagint gives the following translation(s): paidarion —(“little boy; boy; child; young slave”); neos (“novice”); neaniskos —(“youth; young man; servant”); paidion (“infant; child”); pais (“child”); and neanias (“youth; young man”).

Vine's Expository Dictionary of NT Words [2]

1: Νεότης (Strong'S #3503 — Noun Feminine — neotes — neh-ot'-ace )

from neos, "new," occurs in  Mark 10:20;  Luke 18:21;  Acts 26:4;  1—Timothy 4:12 (in some mss.,   Matthew 19:20 ).

King James Dictionary [3]

Youth n. Yuth. G.

1. The part of life that succeeds to childhood. In a general sense, youth denotes the whole early part of life, from infancy to manhood but it is not unusual to divide the stages of life into infancy, childhood, youth, and manhood. In this sense the word can have no plural.

Those who pass their youth in vice, are justly condemned to spend their age in folly.

2. A young man. In this sense it has a plural.

Seven youths from Athens yearly sent--

3. A young person, male or female. 4. Young persons, collectively.

It is fit to youth to read the best authors first.

Webster's Dictionary [4]

(1): ( n.) A young person; especially, a young man.

(2): ( n.) The part of life that succeeds to childhood; the period of existence preceding maturity or age; the whole early part of life, from childhood, or, sometimes, from infancy, to manhood.

(3): ( n.) The quality or state of being young; youthfulness; juvenility.

(4): ( n.) Young persons, collectively.

(5): ( pl.) of Youth

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [5]

The ancients considered youth in a much more extended view than we do. They regarded it relatively with strength, activity, vigor; and while a man retained those attributes he was reckoned a young man, or a youth, without reference to the number of his years. Thus Benjamin is viewed as a mere youth when upwards of thirty years old.. So in  Numbers 21:28, Joshua is called a young man when about forty. The word frequently translated in our version young man is בָּחוּר , Bachur, from בָּחִר , Bachdr, "to choose;" it signifies primarily a choice man one who may be chosen for some particular qualities. (See Lad).