I've collected some numbers from the compilation timeline and the profiles of Vincent, Sephiroth, and Genesis. See if you can come up with a number that reconciles all this:
Approximations:
- Vincent was born "approximately 50 years" before Dec. 0007.
- Vincent slept for "roughly 20 years"/"over 20 years."
- The events of Jenova Project S occurred "approximately 25-30 years" before Dec. 0007.
- Sephiroth was born "approximately 25-30" years before Dec. 0007.
- Sephiroth was born "approximately 20 years" before Nov. 0000.
- The Wutai war began "approximately 8 years" before Nov. 0000.
- Sephiroth and Genesis are "about the same age." Genesis is older than Sephiroth, probably by about a year.*
- Genesis is "around 25" in his CC profile, which might span all of 0000-0007.
Constants:
- Vincent was 27 years old when he stopped aging during Jenova Project S.
- Sephiroth was born during Jenova Project S, when Vincent was 27 or possibly 26.
- Sephiroth was already a SOLDIER in 1997.**
- Sephiroth was recognized as a hero by 0000.
- Vincent briefly awoke on Dec. 19, 0006.
- Gast wrote detailed journals on the events of Jenova Project S.
- Gast fled ShinRa in 1980.
*This logic comes from the CC Q&A that says "Angeal and Genesis were created at roughly the same time, and were deemed as failed projects when they were babies. Project S took the results from Project G and added further improvements, so Sephiroth’s birth was later than Angeal and Genesis’," assuming Sephiroth was not concieved until after Angeal and Genesis were deemed failures as babies.
**This logic comes from the timeline info that says Zack was determined to become a SOLDIER in 1997, and the info from the UO that says Sephiroth was the first SOLDIER. Ergo, if SOLDIER existed in 1997, Sephiroth was a SOLDIER in 1997.