The Australian Open is proving age is just a number

A 25-year-old tennis player in a Grand Slam semifinal shouldn't be considered the baby of the group, especially by a landslide, but that's exactly what's happening in Melbourne right now.

The men's draw is down to four: 35-year-old Roger Federer, 31-year-old Stan Wawrinka, 30-year-old Rafael Nadal and Grigor Dimitrov, the youngest at 25.

By taking out fellow over-30 player Tomas Berdych and No. 5-seeded Kei Nishikori, Federer's comeback from six months off in 2016 should be considered complete.

He will face Wawrinka in a much-anticipated semifinal after Wawrinka bested fellow 31-year-old Jo-Wilfried Tsonga in the quarterfinals.

Nadal is the youngest of the 30-somethings left in the draw and will face Dimitrov on Friday in what will help determine whether youth really trumps age, or vise versa.

The women's draw is almost an exact replica in years with 36-year-old Venus Williams, 35-year-old Serena Williams, 34-year-old Mirjana Lucic-Baroni and, representing the Millennials, 25-year-old CoCo Vandeweghe.

Venus Williams has defied the odds, overcoming illness and injures over her long career to reach her 20th Grand Slam semifinal. Her younger sister Serena has gone about business as usual, reaching her 10th straight major final four.

She will take on Lucic-Baroni, who has stolen hearts as the fairy tale story of the fortnight, bursting into the semifinals 18 years after reaching the same round at Wimbledon back in 1999.

Interviewer Sam Smith said it best, "Girl, mid-30s are happening."

That leaves Vandeweghe, the only 20-something in the women's draw to survive this long in Melbourne. She's competing in her first major semifinal against a player she chased down for an autograph years ago, Venus Williams.

In the end, an aged 30-plus player is guaranteed to vie for the singles title in both draws, proving that the sport is changing, and you don't always need youth on your side to dominate at a Grand Slam.