Green’s Dictionary of Slang

young, unsophisticated, childish.

1908		‘O. Henry’ ‘A Lickpenny Lover’ in Voice of the City (1915) 29: Carter humored her. He had come to know her varying, thistle-down moods.
1916		J. Lait ‘Charlie the Wolf’ in Beef, Iron and Wine (1917) 38: The Chief’s star thistledown ‘dicks’ were conversing.