Gentlemen gentlemen, your disagreement stems in retcon.
FF7:
Vincent: "I'm against it! Why experiment on humans?"
Hojo: "She and I are both scientists."
- cue Lucrecia lowering her head -
DoC:
Vincent: (to Lucrecia) "But using your own child for an experiment?"
Hojo: "HA! I don't know what you're implying, but both of us are scientists. We know what we are doing."
- cue thinly veiled baby daddy drama
-
~~
FF7:
Vincent: ""I was unable......to stop Professor Gast and Hojo... And Lucrecia... I was
unable to stop them... All that I was able to do was watch... That is my punishment..."
DoC:
Vincent: "All I did was watch... I didn’t even try to stop her...and then..."
~~
FF7:
Gast was seen walking into the mansion with the other three at the beginning of Vincent's flashback.
CC Q&A Interview:
"Q2-1: What is the time difference between the start of Jenova Project S and Jenova Project G? And out of Genesis, Sephiroth and Angeal, is Genesis the eldest?
A2-1: Project S and Project G began at roughly the same time. They were lead by Hojo and Hollander respectively, and the department head Gast has little participation in either project."
~~
FF7:
Sephiroth: "Hojo of Shinra, Inc. ... An inexperienced man assigned to take over the work of a great scientist."
Sephiroth: "But, even doing this, will never put you on the same level as Professor Gast."
Sephiroth: "Professor Gast, leader of the Jenova Project and genius scientist, produced me."
Sephiroth: "Professor Gast... Why didn't you tell me anything? ...Why did you die?"
New Compilation info:
Some profiles imply he was only 25 in FF7, which would mean he was...like 2 and a half when Gast left? At the oldest? And that's if he knocked up Ifalna immediately after running off.