I'm not exactly sure...but in ger previous like she died at 18 and now she's 18 so it kind of makes sense since she is a teen
But i remember her saying that she was just a year younger than caitel when she was still an infant, and caitel was around 26 that time
In her previous life, she died at the age of 25 and this life she is still in her 18.
Really!!.... thanks for correcting
Im beginning to think the author forgot about the aria remembers her past life plot. It would make sense as to why aria acts like her physical age and not her mental age.