I'm not the original poster of this thread. The original posting clearly implies that modern translations of old works do count as old works.
But I think it's worth at least supplementing that approach with the approach that deals with works in their original languages. It seems strange to me to think of a translation that was done by someone who was born in (say) 1986 and that was published this year, as an
old book, whether or not the translator worked with an ancient text.
For example, Sarah Ruden's translations of the Gospels. The original texts are two millennia old but her book just came out two months ago. Is her book an "old book"?
Sarah Ruden is a leading translator of the ancient literature of the West, including both essential Greek and Roman Classics and sacred literature.
sarahruden.com
(This example is offered just to make the point specified -- I haven't forgotten that the original poster, in a subsequent posting, said religious texts shouldn't count for this thread.)
So I think it would be interesting to hear from further contributors here about, sure, ancient works in modern translations, but also about old works in their original language (perhaps with notes and small editorial adjustments in punctuation, capitalization, expansion of conventional contractions, etc., e.g. turning
yt to "that" -- see document linked below).