818-819 (tr. John G. Fitch):
Old men's first weakness is their memory, tired and ebbing away in slow decay.
prima languescit senum
memoria, longo lassa sublabens situ.
But cf. the translation of Frank Justus Miller, which takes prima in a different sense:
early memory grows
through weakness and long disuse.
Emily Wilson's translation sidesteps the problem:
Old folks' minds
get tired and the memory grows dull.
I don't have access to the commentaries of Karlheinz Töchterle (Heidelberg: Winter, 1994) and A.J. Boyle (Oxford: Oxford University Press, 2011).