London - Star Wallaby loose forward Michael Hooper became the second youngest player to 50 Test caps against Argentina last Sunday.
Hooper, who has formed a formidable partnership with fellow loosie David Pocock in recent times, reached the milestone at age 23 years and 361 days.
Only Wales' George North boasts a better record (22 years, 320 days).
Rounding out the Top 5 are former Wallaby wing Joe Roff (24 years, 39 days), French scrumhalf Morgan Parra (24 years, 115 days) and England flyhalf Jonny Wilkinson (24 years, 140 days).
Hooper is expected to be integral to Australia's chances of securing a third Webb Ellis Cup triumph against the All Blacks at Twickenham on Saturday.
Sport24 Editor Garrin Lambley is covering the 2015 Rugby World Cup live from London