olden

Etymology 1

From Middle English olden, probably originally an inflected form of old (compare Old English ealdum, inflected form of eald (“old”)), but later reanalysed as equivalent to old + -en.

adj

1. From or relating to a previous era.
   olden days, olden times
   You are right to some extent in what you say. In the olden days people had a stronger belief in all kinds of witchery; now they pretend not to believe in it, that they may be looked upon as sensible and educated people, as you say. 1886, Peter Christen Asbjørnsen, translated by H.L. Brækstad, Folk and Fairy Tales, page 156
   In olden days, a glimpse of stockings / Was looked on as something shocking; / Now, heaven knows, / Anything goes. 1934, Cole Porter (lyrics and music), “Anything Goes”
2. (archaic) Old; ancient.
   We […] told over the story of past sufferings, and renewed olden vows of devotion. 1857, Martha Griffith Browne, Autobiography of a Female Slave, page 347

Etymology 2

From old + -en.

verb

1. (intransitive, old-fashioned or rare) To grow old; age; assume an older appearance or character; become affected by age.
   They were not worldly days; and so, as we olden with our passage through the world, they stay young, and we love them as pure youthful things are loved. 1912, John Ayscough, Saints and Places, page 123