Laudator Temporis Acti

Theognis 983–988 (tr. Douglas E. Gerber):

Let us give up our hearts to festivity, while they can still sustain pleasure's lovely activities. For the splendour of youth passes by as quickly as a thought. Not so swift are charging horses which, delighting in the wheat-bearing plain, carry their spear-wielding master furiously to the battle toil of men.

ἡμεῖς δ᾿ ἐν θαλίῃσι φίλον καταθώμεθα θυμόν,
    ὄφρ᾿ ἔτι τερπωλῆς ἔργ᾿ ἐρατεινὰ φέρῃ.
αἶψα γὰρ ὥστε νόημα παρέρχεται ἀγλαὸς ἥβη·        985
    οὐδ᾿ ἵππων ὁρμὴ γίνεται ὠκυτέρη,
αἵ τε ἄνακτα φέρουσι δορυσσόον ἐς πόνον ἀνδρῶν
    λάβρως, πυροφόρῳ τερπόμεναι πεδίῳ.

The same, tr. Andrew M. Miller:

Let us devote our hearts to merriment and feasting
    while the enjoyment of delights still brings pleasure.
For quick as thought does radiant youth pass by,
    nor does the rush of horses prove to be swifter
when carrying their master to the labor of men's spears
    with furious energy, taking joy in the plain that brings forth wheat.

I'm not sure who translated these lines in The Cambridge History of Classical Literature, I: Greek Literature, edd. P.E. Easterling and B.M.W. Knox (Cambridge: Cambridge Univerity Press, 1985; rpt. 2003), pp. 141-142:

As for us, let us devote our hearts to feast and celebration, while they can still feel the joy of pleasure's motions. For glorious youth passes by swift as a thought, swifter than the burst of speed shown by horses as they take a chieftain and his spear to the battle line, galloping furiously as they take their joy in the flatness of the wheatfields.

T. Hudson-Williams ad loc.: