Just two days after turning 37, Gallen on Thursday announced he would play on next year and then draw a curtain on his illustrious career.

After months of soul searching and questioning whether he still had another year in him, the Sharks ironman decided he still had plenty left to offer.

He has yet to agree to terms with the Sharks, but will smash the record books when he runs out for a 19th season next year.

Gallen is the current co-holder, along with fellow Sharks great Andrew Ettingshausen and teammate Luke Lewis, for most seasons in the NRL with 18.

And he will move past both of them next year.

"Plenty of people quote my age and the fact that I was 37 earlier in the week," Gallen said.

"However the body feels good, training is still something I look forward to and the feedback from the coach and those that matter say my contribution to the team on game day is strong.

"I've always said age and my birth certificate would never make this decision for me.

"And personally, I believe I've got plenty left to give."

While the Sharks lock's minutes have dropped this year, the former NSW captain has still averaged 133m per game, the seventh most of any forward in the league, according to Fox Sports Stats.

Gallen has played 321 games for Cronulla since debuting in 2001 and captained the side to their first premiership in 2016.

With three games and a finals series to go this year, another season will give Gallen a chance at break through the 350-game barrier.

Cameron Smith (379), Darren Lockyer (355) and Terry Lamb (350) are the only three players to achieve the milestone.

Sydney Roosters halfback Cooper Cronk (343) will join the elite club either this year or early next season.

Heading into Saturday's clash with North Queensland, the Sharks are well entrenched in the race for a second premiership in three years in sixth spot.

Should the Sharks lift the Provan-Summons trophy, Gallen will become the oldest player in 96 years to be crowned a premiership winner.

"As for the terms and the contract, I'll sit down with the club at the end of the year and sort out the details," Gallen said.

"But at this stage we're concentrating on the Cowboys first, then the big games we have coming up after that.

"I can say that 2019 will be my last season, I now have an end date."

Australian Associated Press