the world > life > source or principle of life > [noun] > course or span of life > as a measure of time (3)
= generation, n. 3. Obsolete.
A lifetime taken as a rough measure of time; a generation. Usually in plural. Now archaic and literary except as merged with sense 8a.
The average time it takes for children to grow up, become adults, and have children of their own, generally considered to be about thirty years…