despite being ...; unbecoming of ...; in a way uncharacteristic of ...
Attaches to nouns (often 女, 男, 子供, 学生, etc.) to express that an action is inappropriate or unexpected for that role or status. Most commonly seen as 女だてらに. Carries a critical or old-fashioned tone.
It's unbecoming of a woman to use such rough language.
子供だてらに大人の議論に口を出すなんて生意気だ。
It's impertinent for a child to butt into an adult discussion.
Unbecoming of a woman, she carried the heavy load by herself.
Despite being a student, he lives an extravagant lifestyle.
despite being a woman; unbecoming of a woman; in an unladylike way
Derived from the noun 立て (たて, 'position' or 'status') + ら (plural/approximating suffix) + に (adverbial particle). The exact historical development is uncertain, but it has long been used to express incongruity with one's social standing.