The title translates to "25-year-old Girl's High School Student" or more accurately, "The 25-year-old High School Girl". It's a Japanese manga and anime series written and illustrated by Aya Nakahara.
"25-sai no Joshikousei"!
The anime adaptation consists of 13 episodes and was well-received by audiences for its unique premise, relatable characters, and lighthearted tone. 25-sai no Joshikousei