Charles Ellicott Commentary Leviticus 27:5

"And if it be from five years old even unto twenty years old, then thy estimation shall be of the male twenty shekels, and for the female ten shekels." — Leviticus 27:5 (ASV)

If it be from five years old, even unto twenty years. — From the fact that a child of five years is mentioned here, it is evident that the vows spoken of here are not simply those which a person makes regarding themselves, but also those which they make for others, since a vow made by a child involving the payment of a considerable sum of money was not binding. The case, therefore, considered here is that of a father or mother vowing their male child to the Lord, or of any other person taking it upon themselves to pay the value of such and such a child to the sanctuary. This is even more manifest from the following verse.

The male twenty shekels. — Since the services of a boy at the age specified here are of much less value, the parent, or anyone else, who vows him to the sanctuary, is to pay £2 11s. 8d.

The female ten shekels. — For the girl, whose value is proportionately less, the vower is to pay £1 5s. 10d. This is the same value placed on an old woman .