Green’s Dictionary of Slang

grommet n.²

1. (Aus.) a surfer.

1985		in Tracks (Aus.) Dec. 3: I have known one grommet [...] who is really dedicated and takes his surfing seriously.
1990		T. Winton Human Torpedo 12: He could sure ride a board. Genuine surf rat, grommet extraordinaire.
1993		B. Moore Lex. of Cadet Lang. 178: grommet [...] In the wider community the term may be used to refer to surfers in general, not just to tyros.
2002		S. Maloney Something Fishy (2006) 94: The surf scene [...] was tight and the local nazis took a dim view of blow-in grommets.
2009		D. Boyd Legends of Surfing 24: Bluey, who of course was a redhead, started out surfing on his mom’s ironing board when he was a grommet of six years of age.

In compounds

grommet dude (n.)

(N.Z. teen) a boy.

2003

McGill Reed Dict. of N.Z. Sl.