and I'm under the impression that every powerful(ish) yao is old, because of how long it takes for them to cultivate

Yeah, agreed, that's definitely a thing.

SW is doing this in ZYL's apartment when the cutting has nothing to do with ZYL?

Yes! That's a great point. I mean, he's there because he agreed to stay with ZYL for one more night (that's in the dialogue), but either the cutting was so urgently necessary that he couldn't wait a moment longer, or he just couldn't bring himself to leave - but at the same time, him being there for no reason in particular just really makes it obvious how much they're basically living together at this point. ♥ ♥ ♥