EDIT: Replaced my paragraph with the chart below; seems easier to read.

3rd (20-30) -> Orochi, Jiraiya, Tsunade (10-12)
Orochi (20-25) -> Anko (10-12)
Jiraiya (25-30) -> 4th (15-ish?)
4th dies at 23, making Jiraiya 38
Jiraiya (50) -> Naruto (12)

Add 38 to the initial range of age for the 3rd, and you get 58-68 for the age of the 3rd when he croaked.

Sounds reasonable to me.

NOTE: All ages are speculation. But it sounds right to me.