According to Victor Hugo, forty is the old age of youth.
The quote "Forty is the old age of youth; fifty is..." comes from Victor Hugo, highlighting a perspective on the aging process and the transition between different stages of life. The reference [Forty is the old age of youth; fifty is... Victor Hugo - Forbes Quotes.] confirms this answer. Essentially, Hugo suggests that the youthful period of life concludes around the age of forty.
