Quotations about   timing

Therefore it is fitting for the women to be married at about the age of eighteen and the men at thirty-seven or a little before — for that will give long enough for the union to take place with their bodily vigor at its prime, and for it to arrive with a convenient coincidence of dates at the time when procreation ceases. Moreover the succession of the children to the estates, if their birth duly occurs soon after the parents marry, will take place when they are beginning their prime, and when the parents’ period of vigor has now come to a close, towards the age of seventy.

Aristotle (384-322 BC) Greek philosopher
Politics [Πολιτικά], Book 7, ch. 16 / 1335a.27 [tr. Rackham (1932)]
    (Source)

Alt. trans.:

And so it is best to unite women of about eighteen years of age and men of thirty-seven or less; for by such an arrangement the union will be during their greatest physical perfection, and will, as the years pass reach the limit of child-begetting at the right time. Again, the succession of children will be secured, as the younger generation will be having children at the beginning of their prime, supposing some to be born at once, as we may expect, and as the right age has passed away from the older generation as they approach the limit of seventy years.
[tr. Bolland (1877)]

Women should marry when they are about eighteen years of age, and men at seven and thirty; then they are in the prime of life, and the decline in the powers of both will coincide. Further, the children, if their birth takes place soon, as may reasonably be expected, will succeed in the beginning of their prime, when the fathers are already in the decline of life, and have nearly reached their term of three-score years and ten.
[tr. Jowett (1885)]

For which reason the proper time for a woman to marry is eighteen, for a man thirty-seven, a little more or less; for when they marry at that time their bodies are in perfection, and they will also cease to have children at a proper time; and moreover with respect to the succession of the children, if they have them at the time which may reasonably be expected, they will be just arriving into perfection when their parents are sinking down under the load of seventy years.
[tr. Ellis (1912)]

Hence it is fitting for women to unite in marriage around the age of eighteen, and for men at thirty-seven or a little before. At such an age, union will occur when their bodies are in their prime, and will arrive at its conclusion conveniently for both of them with respect to the cessation of procreation. Further, the succession of the offspring -- if birth occurs shortly after marriage, as can reasonably be expected -- will be for them at the beginning of their prime, while for the fathers it will be when their age has already run its course toward the seventieth year.
[tr. Lord (1984)]