I saw on the wiktionary definition of ‘iuvenis’ that the ages it corresponds to are roughly 20-40; however, the ‘vir’ definition does not say to which ages it corresponds. So, at what age does a ‘iuvenis’ become a ‘vir’?
It’s not a strict gradation, so information in different books may be confusing.
Puer:
- infans: 0-7
- puer: 7-16 (7-15 in Ramshorn; 7-15/17 in Forcellini)
- ἔφηβος: after 16
- adolescens: 16-18 (12-21 in Dumesnil; 15-30 in Ramshorn; under 28 in Forcellini)
Juvenis (under 40 in Dumesnil; under 45-50 in Ramshorn; under 50 in Forcellini):
- (adolescens): 18-24
- juvenis: 24-30
- vir: 30-40
Maturus:
- (vir): 40-50
- vetus: 50-60
- senex: 60-
Pay attention to the fact, that “juvenis” has two meanings according to Döderlein.
Hand-book of Latin Synonymes, Döderlein (1875):
Puer (from parere, πάϊς,) in a wider sense, is the man in his dependent years, so long as he neither can be, nor is, the father of a family, as a young person, in three periods, as infans, νήπιος, παιδίον, from his first years till he is seven; as puer, in a narrower sense, παῖς, from his seventh year till he is sixteen; as commencing adolescens (from ἄλθειν) a youngster, μειράκιον, νεανίας, from his sixteenth year. Juvenis, in a wider sense, is as long as he remains in his years of greatest strength, from about the time of his being of age to the first appearances of advanced age, as the young man νέος, which also may be divided into three periods;—as ceasing to be adolescens, from his eighteenth year; as juvenis (from ζέω) in a narrower sense, νεανίας, from his four-and-twentieth year; as beginning to be vir, ἀνήρ, from his thirtieth year. Maturus is the man in his ripest years, when the wild fire of youth has evaporated, and may be divided into three periods;—as ceasing to be vir, ἀνήρ, from his fortieth year; as vetus, γέρων, from his fiftieth year; as senex, (ἄναξ) πρεσβύτης, from his sixtieth year.
Also, look for aetas in Forcellini.