Few people remember having been young, and how hard they found it to be chaste and sober.

[Peu de gens se souviennent d’avoir été jeunes, et combien il leur était difficile d’être chastes et tempérants.]

Jean de La Bruyère (1645-1696) French essayist, moralist

The Characters [Les Caractères], ch. 11 “Of Mankind [De l’Homme],” § 112 (11.112) (1688) [tr. Stewart (1970)]
    (Source)

(Source (French)). Alternate translations:

Few people remember that they have been young, and how hard it was then to live chaste and temperate.
[Bullord ed. (1696)]

Few People remember they have been Young, and how hard it was then to live Chaste and Temperate.
[Curll ed. (1713)]

Few remember that they have been young, and how hard it was then to live chaste and temperate.
[Browne ed. (1752)]

Few men remember that they have been young, and how hard it was then to live chaste and temperate.
[tr. Van Laun (1885)]