Age-defying Roger Federer says after winning his third Grand Slam title in a year he has no idea how long he will continue playing.

The 36-year-old Swiss marvel continues to defy the years and attrition rate, reaching his 30th Grand Slam decider and claiming his sixth Australian crown and 20th Grand Slam title.

The World No.2 won back-to-back Australian Opens by beating Marin Cilic 6-2, 6-7 (5/7), 6-3, 3-6, 6-1 on Sunday, dropping his only sets of a stress-free tournament.

Federer, who downed great rival Rafael Nadal in a classic five-set Australian final Lin 2017, eased through this year’s event with five of his seven matches finishing on or under two hours and he spent just a total of 13hr 53min on court.

Asked after his Melbourne triumph how much longer he can continue at the summit of men’s tennis, he replied: “No idea.

Honest, I don’t know. I have no idea.

“I’ve won three slams now in 12 months. I can’t believe it myself. I just got to keep a good schedule, stay hungry, then maybe good things can happen.”

Federer said his age didn’t come into it when questions were raised about his continuing longevity.

“I don’t think age is an issue, it’s just a number,” he said. “But I need to be very careful in my planning, really decide beforehand what are my goals, what are my priorities.

“I think that’s what’s going to dictate how successful I will be.” But he added: “Exciting times ahead. As a professional, it’s what we do. But I’m happy I’m in that position right now.”

His emotional victory in Sunday put him alongside Novak Djokovic and Australian Roy Emerson with the most Australian titles at six.

While his long-time rivals Nadal, Djokovic, Stan Wawrinka and Andy Murray have injury concerns heading into the new season, not only did Federer blaze on into the final but he finished stronger than Cilic, who is seven years younger, in the fifth set.

Federer was the oldest man at 36 to reach the Australian Open final since Australians Ken Rosewall (37) and Mal Anderson (36) played in the 1972 decider.

He explained his circumstances which allowed him to play on.

“I think by not overplaying, not playing every tournament possible. I enjoy practice. Not minding the travel. Having a great team around me, they make it possible,” he said.

“At the end it’s seeing that my parents are incredibly proud and happy that I’m still doing it. They enjoy coming to tournaments. That makes me happy and play better.”

Federer is the father of two sets of twins, Myla Rose and Charlene Riva and Leo and Lenny with wife Mirka, a former player he met at the 2000 Olympics in Sydney.

Despite his win Federer will remain world No.2 behind Nadal while Cilic has climbed from six to a career-high three.

Cilic overcame Federer on the way to winning the 2014 US Open final, but it remains his only win in 10 encounters.