From a month old, because at that time the first-born, in whose stead the Levites came, Num_8:16, were offered to God, Luk_2:22, and to be redeemed, Num_18:16. And from that time the Levites were consecrated to God, and were as soon as they were capable,’ to be instructed in their work. Elsewhere they are numbered from twenty-five years old, when they were entered as novices to part of their work, Num_8:24; and from thirty years old, when they were completely admitted to their whole office.