time out of mind

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic The distant past beyond anyone's memory.
• noun idiomatic A lengthy duration of time, longer than is readily remembered.
• adverb idiomatic, dated For a lengthy period of time; on numerous occasions.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the distant past beyond memory