Stages of life for a twice-born man

The "stages of life for a twice-born man" are discussed in the Hindu Manusmriti. In essence, this concept argues that a member of the so-called Dhwija (twice-born) castes (Brahmin, Kshatriya, and Vaishya) are to undergo four periods of life: first, as a student Brahmacharya; then, as a householder Grihastha; then, he shall live in retirement Vanaprastha; and finally, as an ascetic Sanyasi. The Manusmriti goes into some detail, regarding what is expected of an invididual during each stage.