There have been around 20 players in the Premier League who made their debuts at 16 years old or younger. By definition if you play in a game you have beaten out other professional players at your club to earn that spot.
Ethan Nwaneri (Arsenal) – 15 years, 181 days old
Harvey Elliott (Fulham) – 16 years, 30 days old
Matthew Briggs (Fulham) – 16 years, 68 days old
Izzy Brown (West Bromwich Albion) – 16 years, 117 days old
Aaron Lennon (Leeds Utd) – 16 years, 129 days old
Jose Baxter (Everton) – 16 years, 191 days old
Rushian Hepburn-Murphy (Aston Villa) – 16 years, 198 days old
Gary McSheffrey (Coventry City) – 16 years, 198 days old
Reece Oxford (West Ham United) – 16 years, 236 days old
Jack Robinson (Liverpool) – 16 years, 250 days old
Jack Wilshere (Arsenal) – 16 years, 256 days old
Angel Gomes (Manchester United) – 16 years, 263 days old
Mark Platts (Sheffield Wednesday) – 16 years, 263 days old
James Vaughan (Everton) – 16 years, 270 days old
Antwoine Hackford (Sheffield United) – 16 years, 288 days old
Wayne Rooney (Everton) – 16 years, 297 days old
James Milner (Leeds United) – 16 years, 310 days old
Samuel Amo-Ameyaw (Southampton) – 16 years, 314 days old
Dane Scarlett (Tottenham Hotspur) – 16 years, 320 days old
Francis Jeffers (Everton) – 16 years, 335 days old
This is just in the English league. Barcelona has given significant playing time to multiple teenagers over the last few years.
The NBA and NFL have age restrictions, but there are routinely guys in the 19-22 age range who come into those leagues and are immediately better than most pros. Victor Wembanyama just turned 20, and he's averaging 20 points, 10 rebounds and 3 blocks per game.