Lewis & Short

sĕneo, ēre, v. n. [v. senex].

  1. I. Lit., to be old (very rare; perh. only in the foll. examples): quamquam aetas senet, Pac. ap. Prisc. p. 887; Cat. 4, 26.
  2. II. Transf., to be weak, feeble: corpus meum tali maerore, errore, macore senet, Pac. ap. Non. 137, 1; (with languere) Att. ap. Prisc. p. 887 P.