from The Century Dictionary and Cyclopedia
- n. Of the age; aged: chiefly used in classic or scholarly epitaphs or obituaries, whether composed in English or in Latin: as, Ob. 1880, æt. (or ætat.) 70: in full Latin, obiit MDCCCLXXX, ætatis (suæ) LXX; that is, he (or she) died in (the year of the Lord) 1880, in the seventieth year of his (or her) age (but usually taken as “70 years of age,” “aged 70”).
Sorry, no etymologies found.