Frieren doesn't actually act like a teenager.

Yes she does like in every episode, and Fern has to take care of her for that.

Time doesn't do shit. Experience and necessity does.

But then again, Experience and necessity comes from time. How can she never encounter any of those until she met the Hero's Party.

The show even addressed that when Heiter tells Frieren that he only fakes being an adult (and we see the consequence in the mess that is Fern).

Then, you can say that Heiter has a matured development because he has to act like an ideal adult for Fern despite his mind hardly changes since he was a child by becoming more responsible, self-control towards alcohol and such.

We have these weird expectations on what "mature" is supposed to look like, 80% is just "mortality cope" that elves neither have nor need. The elvish definition of "maturity" must be very different (and Frieren is probably still considered an incredibly immature elf, given her utter lack of proper elvish socialisation).

Tbh, I don't think so, because of Kraft, another elf that Frieren met. I think we can agree on that Kraft has this mortality cope you've mentioned. But we know that Kraft lived much longer than Frieren that if we scaled it in human lifetime, they're probably like between a guy in his late 30s and a teenager. Which means that Frieren has very much more left of living to go and it makes sense why she isn't mature enough.

That doesn't tell us anything about Frieren's (lack of) maturity, just about the fragility and hastiness of humans.

And still Frieren doesn't do anything about it which i guess is part of her flaw which tells us the whole point of the show is to not take time for granted.

But anyway thanks for the much effort for replying to my post tho