The tradition of addressing young men as "Master"

The tradition of addressing young men as "Master" (e.g., Master David) stems from historical English usage as an honorific for boys and young men not yet considered old enough for the title "Mister". The word "Master" itself has deep roots, tracing back to the Old English term "mægester," meaning "one having control or authority". 

Here's a breakdown of the evolution and reasoning behind this tradition:

Early Usage: Originally, "Master" was a respectful title for men of some rank or authority, such as skilled tradesmen ("free masters" of a guild), employers, or those in positions of learning or leadership.

Forerunner of Mister: Over time, "Master" became a more general term of respect and eventually served as the foundation for the honorific "Mister".

Retained for Boys: As "Mister" became the standard address for adult men, "Master" was retained specifically for boys who had not yet entered society or were considered too young to be called "Mister". This practice of using "Master" for boys gained traction around the early 16th century.

Distinguishing Boys from Men: By the late 19th century, etiquette solidified this distinction, with "Mister" for men and "Master" for boys.

Symbolic of Future Potential: In some contexts, particularly among the gentry or nobility, the eldest son might be referred to as "Master" (or "Young Master") signifying his future role as head of the household and inheritor of the estate.

Declining Usage: While still seen in some formal contexts and traditional circles, the use of "Master" as a prefixed title for boys has largely declined and is considered archaic in many parts of the English-speaking world. 

So, while the term "Master" originally signified authority and skill, it evolved into a way to politely address and distinguish young males from adult men, particularly in formal settings, before largely being supplanted by "Mister."