Green’s Dictionary of Slang

an affectionate term for a small, middle-aged person.

1921		N&Q 12 Ser. IX 383: Bunty. Nickname for a short man.
1953		J. Franklyn Cockney 275: Tich is the most common nickname for a person of small physique; but Bunty is also applied.
1977		D. Powis Signs of Crime 176: Bunty Affectionate term for a small person, especially a small woman of middle age.