Whizzkid: a person who is very good and successful at sth, especially at a young age:
E.g. financial whizz-kids.
Flair for sth: a natural ability to do sth well. SYN talent. E.g. He has a flair for languages
Dab hand: noun(BrE, informal) a person who is very good at doing sth or using sth: E.g. He’s a dab hand at cooking spaghetti. She’s a dab hand with a paintbrush.