(Latin, from juvenis). A youth; common in Shakespeare, thus—
“The juvenal the prince your master, whose chin is not yet fledged.” —2 Henry IV., i. 2.
The English Juvenal. John Oldham (1653-1683). The Juvenal of Painters. William Hogarth (1697-1764).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894