Ne plus ultra

To die of age is a rare, singular, and extraordinary death, and so much less natural than others. It is the last and extremest kind of dying. The further it is from us, so much the less is it to be hoped for. Indeed, it is the limit beyond which we shall not pass, and which the law of nature hath prescribed unto us as that which should not be outgone by any, but it is a rare privilege peculiar unto her self, to make us continue unto it. 

– Michel, Signeur de Montaigne

Why should a man desire in any way 
To vary from the kindly race of men 
Or pass beyond the goal of ordinance 
Where all should pause, as is most meet for all? 

– Alfred, Lord Tennyson

The Montaigne passage is cited as an inspiration to Shakespeare in King Lear (II. iv. 139-41), but how about that line in Tithonus? Seems reasonable to assume Tennyson had read it.