Man is sacrifice. His (first) twenty-four years are the morning-libation. The Gâyatrî has twenty-four syllables, the morning-libation is offered with Gâyatrî hymns. The Vasus are connected with that part of the sacrifice. The Prânas (the five senses) are the Vasus, for they make all this to abide (vâsayanti).

In plain words: A person's whole life is like a sacred offering made in three parts. The first twenty-four years are the morning offering, matching the twenty-four syllables of a sacred verse. These years belong to the Vasus, gods who are really our life-breaths, because they keep us alive.