I calculated she was 7,932 8,374 years old. She was born in the years of the Tree and left for the Grey Havens in the Third Age.
I’d be interested to know if anyone has a definitive answer ;)
Here’s my working outs:
- She was born in the Years of the Trees in 1362 (Valian years1) with 1322 years2 remaining in this age
- There were 590 years3 in the First Age
- There were 3441 years in the Second Age
- There were 3021 years in the Third Age before she left for the Grey Havens
Therefore she’s 8,374 years old. I did a quick check against the Lord of the Ring project’s The Age of Characters in the Lord of the Rings and my calculation of Elrond’s ages (6,520 years old) was pretty close to theirs 6,518. However big caveat, calculating character’s ages in the First Age onwards is easier to do because the years are equivalent to Earth years, unlike the Valinor years which are not.
Source for Middle Earth timeline: Tolkien gateway
1 – A Valinor year is equivalent to 9 Earth Years, 212 days and 18 hours.
2 – There 1500 Valinor years in this age.
3 – Earth years.