Norway's Andreas Fjeld Halvorsen (15) (born 2005) posted a really decent season, stopping the clock at 1:23.26 - 1:53.41 - 3:48.39 and 8:12.82 between 600 and 3000 m. He ran an 8:16.06 in May to break Jakob Ingebrigtsen's Norwegian record for 15-year-olds (he turns 16 in mid September).
Halvorsen improved his 2020 marks from 1:55.72 -> 1:53.71 and 3:56.26 -> 3:48.39 this season.
https://d3n3udvbogpuxv.cloudfront.net/n8mgzupsuv
Feel free to post any other noteworthy American kids or Europeans who are quietly impressing.