(Satipaṭṭhāna Sutta - 54)
And what, bhikkhus, is ageing? It is the ageing, the
getting frail, the loss of teeth, the greying of hair, the
wrinkling of skin; the failing of the vital force, the wearing
out of the sense faculties of beings in this or that class of
beings — this, bhikkhus, is called ageing.
(四念住經 - 54)
復次,諸比丘!老者何耶?於到處之生類中,諸眾生之老,其老耄、齒落、髮白、皮膚皺紋、壽命日滅、諸根衰退。諸比丘!此名為老。