
Her age is around 30 mentally (I'm not sure) and yet she acts like kid.

I felt irked by that too. But then i remembered that shshe lived in the past before ans she described that she was very detached during her first life before. I think she just wants to fill up the things that she missed from before and act according to her body's age to enjoy the moment. But yeah~~ i also think that she should think a little more maturely.

Because she actually didn't live past 30 to act 'mature.' She died in her early 20's and then died again buy younger than that. She pretty much didn't have time to think of her own as a working and responsible person because those things were snatched away from her at such a young age. She didn't have to to establish herself as an adult with responsibilities and all she knows about is now. Maturity doesn't come with age, especially with how much she regressed. That's not how the brain works.

and that's just fuelling the stereotype and problemtic ideology that age comes with experience and that older people are wiser just because they've lived longer. Because of that, a lot of younger people have a hard time finding a job because most people expect them to have experiences and experiences is supposed to come with age. So yeah, it's kinda toxic for ya'll to expect her to act accordingly to her age especially she died young several times and with her experiences in life where she had to grow up all over again.

I kinda agree to you guys however I think that she must've had developed some thoughts in this loop. If timeloop doesn't stop unless she does as the book says that means she's kinda immortal and she can experience different things with that power ( the reason I think like this is that her wanting to go back to her old self feels weak reason. Why she wants to go? Family? Friend? Lover?)
Even if she didn't think about it back then I think she has to now rather than eating cookies all day.

I don't think she's eating all day when most of the time her thoughts are about ML. She also just notice the little details that she didn't know before when she first transmigrated. It was even said that might as well enjoy at being the Viche since in the first timeline she was unfeeling to her father and even ML. She's just enjoying herself now because she never enjoyed her first life as a transmigrator. So no, she can act childish all she wants especially with her situation and even with that, she doesn't stray away from her goal. She practically has to do nothing but just end up dying as long ML turns into a tyrant. You, wanting her to act like an adult is like telling a fresh out of college young adult to have a stable job and life ASAP. Even some adults in their late 20's to early 30's are still adjusting to life and can't be qualified as 'mature' in your standards. You might have a stroke when you find out that millenials are into things that aren't mature. And to not everyone has same experiences into achieving mental maturity, it's different for everybody and you can't just enforce your idea of maturity.
Aw shit here we go again