Although first called up by Joachim Löw for the senior national team in March, Wirtz made his international debut under Flick in the 2-0 win over Liechtenstein in 2022 FIFA World Cup qualifying in September.
That maiden cap at just shy of four months after his 18th birthday makes Wirtz the third-youngest player to appear for Germany since the Second World War, after Uwe Seeler and current international teammate Jamal Musiala.
The Leverkusen midfielder has enjoyed a meteoric rise in the last year and a half. He joined Die Werkself in January 2020 at the age of 16 after a decade in the academy of local rivals Cologne, and quickly found himself in the first-team fold.
In May that year he became the youngest Bayer player in history, making his Bundesliga debut from the start away at Werder Bremen only 15 days past his 17th birthday - some four months earlier than Kai Havertz had played his first game, against the same opponent, in October 2016.
Only 19 days after that, Wirtz scored past now Germany colleague Manuel Neuer to become the youngest goalscorer in Bundesliga history at the time.
Still only 18, his next appearance for Leverkusen will be his 50th for the first team, where he's taken on an ever-greater role at the heart of their play, already reaching double figures for goals and assists.
This summer he also won the UEFA European U21 Championship, including a match-winning brace in the 2-1 victory over the Netherlands in the semi-finals. All performances that clearly impressed Flick enough to call him up with the intention of using him in the senior side.
And now getting to see the midfielder at first hand, the 56-year-old is even more impressed.
"Florian is just a huge asset for this team through his carefreeness," Flick said at a press conference ahead of Germany's qualifier against Iceland. "He's simply an outstanding technician, loves to play, very creative, has a good shot, runs hard and is quick. He's got a good total package."
Wirtz was given half an hour in his second cap when he replaced Marco Reus in the 6-0 win over Armenia. He provided the assist for another teenager, Karim Adeyemi, to complete the scoring.
He's likely to also feature on Wednesday against Iceland before returning to so far unbeaten Leverkusen ahead of the visit of Borussia Dortmund to the BayArena on Saturday.