This paper introduces the notions of age and essence of an infinite wordw. Using these notions, the author studies the setL of infinite non-repetitive words over {1,2,3}, and its proper subsetsL ₁₂₁,L _121,323,L _121,212, where words ofL ₁₂₁ (L _121,323;L _121,212) do not contain 121 (121,323;121,212) as subwords. Motivated by the question How many essentially different nonrepetitive words over {1,2,3} exist? the author counts the equivalence classes ofL,L ₁₂₁,L _121,323,L _121,212 under agreement in a final segment, agreement in age, and in essence.