aren'tyoudaoicibaDictYouDict[aren't 词源字典]
1794, contraction of are not, originally written are'n't and generally so into early 19c.
If "ain't I?" is objected to, surely "aren't I?" is very much worse. [Lady Grove, "The Social Fetich," 1907]
[aren't etymology, aren't origin, 英语词源]