Those replacements are vying to break into an Australia side that is already ageing. Of the team that lost to India in the first Test in Perth, only one player - Nathan McSweeney - was under 30, while four were 34 or over. While age is not necessarily a factor in performance, particularly for a side who are reigning World Test Champions and still who still sit at the top of the ICC's Test team rankings, in terms of sustaining that success amid challenges to their rule, that's where problems seep in.

Australia's fast-bowling trio have underpinned their success and formed a core of the side for the best part of a decade. After Mitchell Starc, Pat Cummins and Josh Hazlewood, the next out and out quick who's played the most Tests for Australia since 2015 is Peter Siddle (11 Tests). Just below Siddle is Scott Boland, who's one of the options to replace Hazlewood in the side in Adelaide.

At 35, Boland is older than all three of the first-choice options. Thus he is not an option to take over as a leader in the attack as the others phase out of the side. The other option Australia have chosen to replace Hazlewood is Sean Abbott who, at 32, is uncapped as of yet at Test level.

In terms of younger pacers with decent first-class experience coming through, it's not hard to see why Australia have turned to those unlikely to be regular faces in the side in two or three years time.

Of those who have been performing decently in Australian domestic cricket, the only player who potentially fits the bill in that regard is Fergus O'Neil, who was part of the Australia A side which faced India A ahead of the senior series. He took four wickets in the third innings of that match, in an attack which also featured Brendan Doggett and Beau Webster, the other additions to Australia's squad for Perth. Of pace bowlers under 30, O'Neil is the only one in the top 15 of the Sheffield Shield top wicket-taker charts so far this year with more than six first-class games under his belt.

Looking at spinners, however, the cupboard appears to be better stocked. Having recently passed his 37th birthday, Lyon has suggested he may continue to play Test cricket after the 2025/26 Ashes series. Despite his plans to extend his career towards his 40th birthday, it's likely Australia will need a regular spinner to replace Lyon in the next two years or so. Todd Murphy has been trialled both in Asia and England with decent levels of success, while Matt Kuhnemann also featured in India last year. It's likely that one of these two will be groomed as Lyon's heir.

Australia have called up uncapped all-rounder Beau Webster to their Test squad as cover for Mitchell Marsh.

Webster’s cricketing journey took a remarkable turn when he switched from spin to pace during the Covid lockdown.

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— Wisden (@WisdenCricket) December 2, 2024

Batters are a trickier equation. Australia drafted in McSweeney as their replacement at the top of the order in Perth, despite the fact he normally bats at No.4 in first-class cricket for South Australia. Having initially bumped Steve Smith up the order after David Warner's retirement, it's a brutal indictment on Australia's domestic top-order pickings that all of them have been overlooked thus far.

The options competing with him for the spot were Marcus Harris (32), Cameron Bancroft (32), Sam Konstas (19), and Matt Renshaw (28). Konstas is the only one of those who hasn't been previously trialled and discarded in that position. While a hugely promising talent, Konstas is barely 19 with 10 first-class games under his belt.

McSweeney failed in Perth, along with every other batter in Australia's top order. That has little bearing on whether he will make a success of his new position, but with options for long-term replacements slim and Usman Khawaja due to turn 38 during the third Border-Gavaskar Test, it's likely that at least one of those options will have to come through over the next few years, regardless of potential longevity or previous lack of success.

There's also an urgency to both Marnus Labuschagne's and Steve Smith's drop in returns. Smith is now almost 18 months post his last Test century, while Labuschagne's struggles have seen his place in the side under question for the first time in five years.

Labuschagne made his Test debut aged 26, while Smith was 21 before emerging as a generational talent around four years later. Travis Head was also in his mid-20s when he became a Test regular. There's a distinct lack of batters pushing for places in Australia's side who fit the bracket their current crop did between five and 10 years ago. While part of that is linked to the success Australia have had with their elite group, it's left them in a tricky position in comparison to other Test sides across the world.

As India's core from the last decade have started to fade, they've successfully brought a new generation into the fold. Yashasvi Jaiswal and Shubman Gill have filled gaps in the top order, while Rishabh Pant's return has bolstered the middle with Sarfaraz Khan waiting in the wings. Nitish Kumar Reddy and Harshit Rana impressed on debut in Perth while India left out their experienced and lethal spinners for Washington Sundar.

India's depth of talent is an exception, but other sides have also had success in drafting fresh and younger talent in over the last few years. The impending doom of James Anderson's retirement was lessened for England by Gus Atkinson's success, while Harry Brook and Jamie Smith have also been brought through as the future. Perhaps Australia fit more in New Zealand's bracket, with their struggles to replace their own fast-bowling trio pronounced.

Maybe this is a problem blown out of proportion. The best years of Khawaja's career have come during and beyond his mid-30s and, until last week, Australia were favourites to make a second successive World Test Championship final. Nevertheless, great Test teams are not only remembered by the trophies and series they won, but by their longevity. To make the jump to that next level, it's one factor they will have to wrestle with.

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