Exodus 24:5

And he sent the firstborn of the sons of Israel,-for until that hour had the firstborn had the (office of performing) worship, the tabernacle of ordinance not (as yet) being made, nor the priesthood given unto Aharon; and they offered burnt offerings and consecrated oblations of oxen before the Lord.

AND HE SENT ‘NA’AREI’ (THE YOUNG MEN OF) THE CHILDREN OF ISRAEL. These were the firstborns, as Onkelos rendered it, for it was they who used to offer the burnt-offerings and the peace-offerings. But I do not know why Scripture designates the firstborns by the term na’arei (the young men)? Perhaps it is because Scripture mentioned the elders who are the nobles of the children of Israel, therefore it called the firstborns ne’arim (young men), for in relation to the elders they were young. It thus indicates that Moses sent them to offer the sacrifices not because of their status in wisdom, for they were not yet advanced in age, but only an account of the birthright, through which they were set aside to offer sacrifices.
In line with the plain meaning of Scripture, the young men of the children of Israel were the youth of Israel who had not tasted of sin, and had never come near a woman, for they were the most select and holy of the people, in a similar manner to that which the Rabbis have said: “The young men of Israel who have not tasted of sin, Note 6). are destined to give forth a fragrance like the Lebanon etc.”” (ibid). The word Lebanon [of the root lavan — white] is an allusion here to the Sanctuary which “whitens” [atones for] the sins of Israel. The thought suggested then is that these young men who have not tasted of sin are as beneficial to Israel as the Sanctuary (Maharsha).

OXEN UNTO THE ETERNAL. The reason they brought oxen is that as long as Israel was in the wilderness they feared the attribute of justice, this being indeed the source of their mistake at the incident of the golden calf — as I will mention there. And so they now offered burnt-offerings and sacrificed peace-offerings all of oxen, for a similar reason to that of the bullock brought by the anointed priest [for a sin-offering], and the bullock which the court brings for an erroneous decision [which contradicts in part what the Torah enjoins],, Verse 14. and the bullock for idolatry, as well as the Red Heifer., 19:2. See Ramban there: “Its redness alludes to the attribute of justice, etc.”

את נערי בני ישראל, the firstborns of each family.