Man comes to each age of his life as a novice.

[L’homme arrive novice à chaque âge de la vie.]

Nicolas Chamfort (1741-1794) French writer, epigrammist (b. Nicolas-Sébastien Roch)

Products of Perfected Civilization [Produits de la Civilisation Perfectionnée], Part 2 “Characters and Anecdotes [Caractères et Anecdotes],” ch. 12 (1795) [tr. Merwin (1969)]
    (Source)

(Source (French)). Alternate translations:

Man arrives a novice at every age of life.
[ed. Mathews (1878)]

Man reaches each stage in his life as a novice.
[tr. Hutchinson (1902), "The Cynic's Breviary"]

A man begins every stage of his life as a novice.
[tr. Parmée (2003), ¶ 422]