How young could a starting XI be in a professional league? Jong Ajax have told you that everything is possible.
In the Netherlands' second division game against Helmond Sport, Ajax II team sent 11 starting players who were all born after 2000. The average age of that squad was 18 years & 204 days. It could be the youngest starting XI ever.
More than that, they beat the rival by 2-0 in that game and now they're on 3rd place of the league. Ajax for the future.