Related Clues:
- Very long stretch of time
- Very long period of time
- A dog's age?
- One billion years equal one
- Simpler spelling of 34-Down
- Big differences between grandparents and grandchildren
- Largest division of time, in geology
- Various numbers among family members
- Very, very long time, in geology
- Years of life
- Vast time period of 1 billion years
- 12,000,000,000 months
- Keeps having birthdays
- At least two geological eras
- Gets long in the tooth