young man who has recently come of age
Archaic term referring to a young man who has just undergone the genpuku (元服) coming-of-age ceremony. Not used in modern Japanese.
See also: 元服
小冠者 is an old word for a young man who has just completed his coming-of-age ceremony.
The exact derivation is uncertain; the kanji 小 (small/young) and 冠者 (capped person) suggest a young person who has received a cap as part of the coming-of-age ritual.