Juventas

From Smith's Dictionary of Greek and Roman Biography and Mythology:

The personification of youth, the Roman equivalent of the Greek Hebe.

From the 1911 encyclopedia:

JUVENTAS (Latin for "youth": later Juventus), in Roman mythology, the tutelar goddess of young men. She was worshipped at Rome from very early times. In the front court of the, temple of Minerva on the Capitol there was a chapel of Juventas, in which a coin had to be deposited by each youth on his assumption of the toga virilis, and sacrifices were offered on behalf of the rising manhood of the state. In connexion with this chapel it is related that, when the temple was in course of erection, Terminus, the god of boundaries, and Juventas refused to quit the sites they had already appropriated as sacred to themselves, which accordingly became part of the new sanctuary. This was interpreted as a sign of the immovable boundaries and eternal youth of the Roman state.

It should be observed that in the oldest accounts there is no mention of Juventas, whose name (with that of Mars) was added in support of the augural prediction. After the Second Punic War Greek elements were introduced into her cult. In 218 B.C., by order of the Sibylline books, a lectisternium was prepared for Juventas and a public thanksgiving to Hercules, an association which shows the influence of the Greek Hebe, the wife of Heracles. In 207 Marcus Livius Salinator, after the defeat of Hasdrubal at the battle of Sena, vowed another temple to Juventas in the Circus Maximus, which was dedicated in 191 by C. (or M.) Licinius Lucullus; it was destroyed by fire in 16 B.C. and rebuilt by Augustus. In imperial times, Juventas personified, not the youth of the Roman state, but of the future emperor.

From The History of Rome By Titus Livius. Book V

Here, when the Capitol was to be freed by the rites of augury, Juventas and Terminus, to the very great joy of our fathers, suffered not themselves to be moved. Here is the fire of Vesta, here the Ancilia sent down from heaven, here are all the gods propitious to you if you stay."