The Japan Society (333 E 47 in NYC) sponsored this spring a lecture given by John T. Carpenter “Amusements in a Samurai Mansion: Male Youths as Actors, Escorts, or Outcasts in Early Edo Art”.

This mysterious mention led me to Wiki, where this was revealed:
“Although any person would be clearly classified as a child, wakashū or adult, the timing of both boundaries of the wakashū period were relatively flexible, giving families and patrons the ability to accommodate the development and circumstances of the individual boy.

The concept of wakashū contained several partially overlapping elements: an age category between childhood and adulthood; the social role of a pre-adult or adolescent boy, usually conceived of as a subordinate (student, apprentice or protégé); and the idea of the “beautiful youth”, a suitable target for homosexual desire and the subject of wakashūdo, “the way of youths”. As boys were considered eligible for homosexual liaisons only when they were wakashū, their patrons occasionally delayed their coming of age ceremony beyond socially acceptable limits, leading to legal efforts in 1685 to require all wakashū to undergo their coming of age ceremony by age 25.[3]

Sources such as Ihara Saikaku‘s Nanshoku Ôkagami (“A Great Mirror of Male Love”, 1687) indicate that “in the past” (when is not precisely clear), wakashu were typically “ostentatiously violent, and thus manly,”[2] and that at that time, a young man who was too weak, gentle, or feminine in his manner would find it difficult to find an older samurai with whom to engage in shûdô. This emphasis on martial manliness is somewhat understandable, given the martial nature of life in the Sengoku period, and the idea that wakashû were expected to grow up to become fathers, warriors, and nenja[3] themselves.

Saikaku indicates, however, that by his own time (the Genroku period, 16881704), wakashû came to be valued more for their youth, beauty, and artistic abilities (e.g. in dance, music, and poetry), and less for their physical strength or martial prowess, in conjunction with the rise of the feminization of young actors on the kabuki stage.[4]