Old English colt "a young horse," also "young ass," in Biblical translations also used for "young camel," perhaps from Proto-Germanic *kultaz (source also of Swedish dialectal kult "young boar, piglet; boy," Danish kuld "offspring, brood") and akin to child. Commonly and distinctively applied to the male, the young female being a filly. Applied to young or inexperienced persons from early 13c.
COLT'S TOOTH An old fellow who marries, or keeps a young girl, is ſaid to have a colt's tooth in his head. ["Classical Dictionary of the Vulgar Tongue," 1796]
The image is in Chaucer. Colts shed their first set of teeth beginning at about three years.
adjectival word-forming element, Old English -isc "of the nativity or country of," in later use "of the nature or character of," from Proto-Germanic suffix *-iska- (cognates: Old Saxon -isk, Old Frisian -sk, Old Norse -iskr, Swedish and Danish -sk, Dutch -sch, Old High German -isc, German -isch, Gothic -isks), cognate with Greek diminutive suffix -iskos. In its oldest forms with altered stem vowel (French, Welsh). The Germanic suffix was borrowed into Italian and Spanish (-esco) and French (-esque). Colloquially attached to hours to denote approximation, 1916.