Related Clues:

• Lotsa time
• Geologic time unit
• Gets mellower
• What seems like forever
• Iron and Bronze, for two
• Piles on birthdays
• Inverted
• A very long period of time
• 365 billion days, in astronomy
• Golden and Bronze, e.g.
• Gets better?
• Several eras
• Shakespeare's seven
• Loses immediacy
• It's quite a stretch