Green’s Dictionary of Slang

(US) a fool.

1848		Boston Blade 17 June n.p.: That particular sweet-scented peep J.S. better be at home with his wife than lounging about Ma’am D’s.
1853		Life in Boston and N.Y. 1 Oct. 3/8: If that peep, who goes by the name of W—n, [...] don’t put a stop to his blowing, he may get himself in trouble. [Ibid.] Those four Micks who hang out in Grand, a few doors from Allen street, make perfect peeps of themselves by putting on such airs.