In FFVII, if Cloud's team visits Lucrecia in the cave, she will say something about wanting to die because of her past but the Jenova in her wouldn't let her die. Maybe that was the reason why she sealed herself inside the crystals in that cave.
What about Lucrecia? She also didn't age from 30 years back. From the flashback in DoC until now, she's still as young as ever. Is it because of the Jenova cells? Hojo did inject the cells into Vincent's body. I could be wrong about this, though.