Related Clues:
- Nears retirement
- 1 billion years
- Important periods
- 365 billion days, astronomically
- Interminable stretch
- They may be checked at the door
- Almost eternity
- Longish span of time
- Millennia on end
- Bronze and Iron, e.g.
- Ever so long
- Geological span
- Becomes drinkable, perhaps
- Grows old gracefully
- Iron and Bronze, e.g.