What ages do you address young boy as master?

After its replacement in common speech by Mister, Master was retained as an address for boys or young men. By the late 19th Century, etiquette dictated that men be addressed as Mister, boys under 8 years old be addressed as Master, and from 8 to the age of maturity males not be accorded courtesy titles. However, in more recent times it is not uncommon for high-school boys (and sometimes junior-high-school boys, but not, typically, younger) to be addressed as Mister, though some etiquette writers hold that the title Mr should not be used until the boy has left school. The title Master is much less frequently used in spoken language than formerly. However, Master is still used as the written form of address for boys of some undefined age, often regarded as under 8 in formal correspondence, particularly invitations to formal affairs.