Ibn Ezra on Numbers 11:28

מבחוריו. יש אומרים שפירושו מבחרותו והטעם שלא אמר כדברי זקן ויש מדביקים מבחוריו עם משרת משה והטעם ששרת אותו מיום שהיה בחור וזה איננו נכון כי זה המעשה היה בשנה השנית והנכון בעיני שהוא מבחוריו הוא מהמובחרים לשרת משה כי אחרים יש עמו ודע כי מלת בחור בלשון רבים פעם תשתנה ופעם לא תשתנה וכן מלת סריס אולי הם שני משקלים: FROM HIS YOUTH UP. Some say that the meaning of mi-bechurav (from his youth up) is, from his youth. It means that he did not speak as an elder speaks.¹¹⁷He spoke as a youth speaks. Others connect mi-bechurav (from his youth up) to mesharet mosheh (the minister of Moses);¹¹⁸They read our text as follows: mesharet mosheh mi-bechurav, meaning the minister of Moses from his (Joshua’s) youth on. this means the one who served Moses from the time of his youth.¹¹⁹So Onkelos and Rashbam. However, this is incorrect, for this event occurred in the second year.¹²⁰Following the Exodus. However, Scripture nowhere tells us that Joshua served Moses before this date. In my opinion, the word mi-bechurav means from the chosen. It means that he was one of those chosen to serve Moses, for there were others with him.¹²¹According to I.E. our clause should be interpreted: And Joshua the son of Nun, the minister of Moses, one of his chosen, answered and said. Note that the word bachur (youth, or chosen) sometimes changes in the plural and sometimes does not.¹²²In the plural the word is at times vocalized with a pattach (Ps. 78:31) and at other times with a sheva as in our verse (bechurav, rather than bachurav). The same applies to the word saris (officer).¹²³The plural of saris is both sarisim (Esth. 2:21) and serisim (Gen. 40:7). It is also possible that they belong to two different paradigms.¹²⁴Bachurav comes from the singular bachur (vocalized pattach, shurik), bechurav from the singular bachur (vocalized kamatz, shurik). Similarly sarism, and serisim. According to rules of Hebrew grammar, in the former form the kamatz changes to a sheva in the plural. Compare, davar, devarim. However, in the latter case the pattach is maintained in the plural form.

כלאם. נפתח הלמ"ד בעבור אות הגרון הבא אחריו: SHUT THEM IN. The lamed of kela’em (shut them in) is vocalized with a pattach¹²⁵That is, a kamatz. There is either a scribal error or I.E. refers to a pattach here by the term kamatz. He occasionally does so in his long commentary on Exodus. because a guttural¹²⁶An alef. follows it.¹²⁷Compare, kara’em, shelachem.