Matthew Henry Presbyterian @wholebiblehenry

Here is the exchange made of the Levites for the first-born. 1. The first-born were numbered from a month old, Num 3:42, Num 3:43. Those certainly were not reckoned who, though first-born, had become heads of families themselves, but those only that were under age; and the learned bishop Patrick is decidedly of opinion that none were numbered but those only that were born since...

Commenting on Numbers 3:40-51

John Gill Reformed Baptist @doctorgill

And all the firstborn males,.... For such only were ordered to be numbered, and not firstborn females: by the number of names; which were particularly taken: from a month old and upward; for before that time they were not sanctified to the Lord, nor subject to the redemption price: of those that were numbered of them were twenty and two thousand two hundred and threescore...

Keil & Delitzsch Lutheran @keilanddelitzsch

Num 3:40-48 After this, Moses numbered the first-born of the children of Israel, to exchange them for the Levites according to the command of God, which is repeated in Num 3:41 and Num 3:44-45 from Num 3:11-13, and to adopt the latter in their stead for the service at the sanctuary (on Num 3:41 and Num 3:45, cf. Num 3:11-13).

Commenting on Numbers 3:40-48