User blog comment:CNBA3/Chapter 474 Review/@comment-119.74.151.113-20160222145502/@comment-7418318-20160222153827

Between working on plants (which are also alive), unlocking Second Origin in people and effecting everything on the planet including the living beings, that "rule" of Ark of Time seems to be far from absolute.

It's quite possible that instead of a rule, it was just something that Ultear hadn't managed to master back then, or that instead of being impossible it carried dire consequences that she was unwilling to risk. But now with her body being close to dying, she might not care about those consequences anymore.

I too think the age vamprirism is very unlikely - and as you said would suck from a storytelling perspective - but we can't fully rule it out either.