νεᾱν-ῐεύομαι · nean-ieuomai — LSJ
to be a youth
to be a youth, Ph. 1.303, Poll. 2.20.
II act like a hot-headed youth, wilfully, wantonly, swagger, behave so, with youthful insolence, wanton acts
more freq., act like a hot-headed youth, wilfully or wantonly, swagger, Ar. Fr. 827, Lys. Fr. 324 S.; ν. εἰς τοὺς πολίτας behave so towards . . , Isoc. 20.17, cf. Hyp. Eux. 27; ἐν τοῖς λόγοις Pl. Grg. 482c; νεανιευσάμενος εἰπεῖν with youthful insolence, Plu. Cic. 1:— Pass., ἐφʼ ἅπασι τοῖς ἑαυτῷ νενεανιευμένοις to all his wanton acts, D. 21.18; τὰ ἐν τῇ βουλῇ νεανιευθέντα Plu. Mar. 29.
2 make youthful, bold, promises, undertake with youthful spirit
make youthful, i.e. bold, promises, c. Adj. neut., ν. τοιοῦτον, ὡς . . D. 19.194; οὐδʼ ἐνεανιεύσατο τοιοῦτον οὐδέν Id. 21.69; μέχρι τοῦ λόγου ν. Luc. Bis Acc. 21: c. inf., undertake with youthful spirit, Plu. Dem. 3.