At least not initially, i think her age was more of gimmick, but it would be interesting if it's incorporated into the story and turned out that she is non-fully-human so she and her daughters don't die within the normal human lifespan.
It's a pretty common theory (that I also believe in) that there's some sort of timeloop shenanigans going on in the story. Plus time in Kredon seems weird; the weather is bizarre and Annie mentions that hair grows really quickly in Kredon. I sometimes wonder whether Kredon isn't just an Eternum server and the whole cast are NPCs. I think the MC himself is clearly brainwashed in some capacity, he's got suppressed memories and keeps repeating "I hardly ever dream in the first place" every time he has a dream.
I think the timeloop (if it exists) erases memories but not emotions, so they get reinforced each loop.
- In the sex scene with Nancy in the elevator she says she's wanted to have sex with the MC since she saw him in the park, which is a little odd.
- In the blowjob scene with Dalia in the Cove she mentions the MC's cum tastes exactly as she imagined, which is also a little odd.
- In the latest update if you romance Calypso the MC will mention that kissing her felt like something that was meant to happen.
- The MC knows stuff about the love interests he should have no way of knowing (favourite foods, movies, etc), Dalia even calls him out about knowing her favourite movie is the Lord of the Rings trilogy.
On the original point about Calypso outliving everyone, I guess the easiest answer would just be to say that everyone aren't humans, but are instead human looking "eldari" like the ones she said were in the story about Queen Anima.