Ex-NRL star into Group 2 grand final at 46

Former NRL player Brandon Costin has rugby league officials scrambling through the record books after guiding the Coffs Harbour Comets into the Group 2 grand final at age 46.

Officials believe Costin - who played 136 ARL/NRL games for South Sydney, Western Suburbs, Sydney Roosters and Canberra before finishing his top-flight career in England - is one game away from becoming the oldest premiership winner in Country Rugby League history.

Sharing a co-coaching role, Costin only laced on the boots again on Sunday because of an injury crisis at the club.

But the veteran produced a stunning performance in Coffs Harbour's 32-18 major semi-final win over the Danny Wicks captain-coached Grafton Ghosts, the minor premiers and 2017 Claytons Cup winners as the most dominant side in NSW Country Rugby League.

"It was unbelievable," Comets life member and historian Neil MacAlpine told AAP.

"He played about 25 minutes either side of halftime, set up one try and then scored a 70-metre runaway try.

"It was phenomenal, just freakish. The crowd just erupted."

According to MacAlpine, Costin's four-pointer came 28 years after his last first-grade try in Comets colours as an 18-year-old.

"But the previous week he scored four in reserve grade when we flogged the Ghosts 80-0," MacAlpine said.

"He's still in great nick. He does a lot of cross-fit training."

The Comets have only won one of eight grand finals since 1985 but await the winner of the Ghosts versus Macksville preliminary final to learn who they face in this year's big one.

It remains to be seen whether Costin pulls on the boot once more.

"Needless to say, we've already appointed Brandon as coach again next year, regardless," MacAlpine said.

That's much to the displeasure of his wife Cheree.

"I'm not really a fan of footy so I'll be glad when it's finally all over. Unfortunately, that could be never," she said.

"I think he's retired five times."