Related Clues:

• Atomic and Ice, e.g.
• Time immemorial
• Middle and Stone
• Periods
• Wrinkles, say
• A really long time
• Long period
• Mellows, as wine
• A very long time
• Shakespearean seven
• Shakespearean septet
• Periods in history
• Many, many years
• An eternity
• Word with Dark or Middle