Hinkley also scored a try on his debut for England under-20s in a bonus point win against Wales in the 2018 Six Nations Under 20s Championship. He was in the England squad for the 2018 World Rugby Under 20 Championship and appeared as a replacement in the defeat against France in the final. He played every minute of the 2019 Six Nations Under 20s Championship, winning two man of the match awards in the tournament and scoring a try against Scotland. He started every game of the 2019 World Rugby Under 20 Championship, scoring a try against Australia as England finished fifth.