Supplementing the examples identified in Hugo's answer, I note the following earliest matches in Early English Books Online searches for "olden day[e]s"—from George Gascoigne, The Steele Glas: A Satyre (1576):

I speake not this, by any english king, / Nor by our Queene, whose high for sight prouids, / That dyre debate, is fledde to foraine Realmes, / Whiles we inioy the golden fleece of peace. / But there to turne my tale, from whence it came, / In olden dayes, good kings and worthy dukes, / (Who sawe themselues, in glasse of trusty Steele) / Contented were, with pompes of little pryce, / And set their thoughtes, on regal gouernement.

and "olden times"—from Joseph Bentham, "The Seventh Meanes and Duty Is Sanctifying the Lords Day," in The Saints Societie Delivered in XIV. Sermons (1636):

Secondly, whereas many unguard the doores of their lips, and suffer those little unruly members to enflame each others, (ministring and taking occasions offered) extravagantly to wander into olden times, gladding themselues with their large discourses of their many madde, and merry meetings, their frolique frisques, and gambols, their infamous exploits, and deeds of darknesse: or idly to range about, from royall diademe to the penylesse cottage, from field to towne, from towne to houses, from houses to particular things and persons; yea, to their owne homes, and houses; taking thence many large, and deepe discourses of the number, and severall conditions of their sheepe, horses, &c. the unrulinesse of this; the faire conditions of that; the great penyworth they had in the one, the worth of the other; ...