Billy is certainly a precocious talent, as Wiki details:
"Gilmour developed his career as part of
Rangers Academy. His progress saw him fast-tracked towards the first team, making his debut for the under-20 development team in December 2016 at the age of 15 and being invited to train with the first team squad the following month by manager
Mark Warburton."
Into Rangers' first team at the tender age of 15 and then on to Chelsea the following year to develop through the academy.
"He made his
Premier League debut on 31 August 2019 against
Sheffield United, coming on in the 84th minute for
Tammy Abraham. He made his full debut on 25 September, playing the full 90 minutes in a 7–1
EFL Cup win against
Grimsby Town. He was added to the Chelsea first-team squad on a permanent basis in February 2020. He was widely praised for his performance in a 2–0 win against Liverpool in an
FA Cup tie on 3 March. Gilmour would later make his first Premier League start later that week on 8 March against
Everton, earning Man of the Match honours in a 4-0 win. He did not play much for the next six months or so, due to the lockdown caused by
COVID-19 and a knee injury. Gilmour made 11 appearances for the Chelsea first team during the 2019–20 season."
He was called up to the Scotland squad at the age of 19 and featured in 3 Euros matches, culminating in his man of the match performance against England.