Online Etymology Dictionary

colt (n.): Old English colt "colt," originally "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. Applied to 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]
Colt (n.): type of revolver, 1838, originally the manufacture of U.S. gunsmith Samuel Colt (1814-1862).