Young gun suggest a prospect or star as in 'Gun' Cricketer
or alternatively, a young 'un who as a person looking to have a career in sport is / percieved to be a bit of a potential 'sharp shooter' (at some point) and is seen, by some, as a young gun, perhaps?
in common use in the UK , the term young gun , applied to young professional/ aspiring to be professional footballers ..... below,links to a trio of many examples
Our 16-year-old goalkeeper discusses life in north London, training with the first team and learning from Mart Poom
www.arsenal.com
AARON Ramsey will become Cardiff City’s newest senior professional on his 17th birthday next month.
www.walesonline.co.uk
He was spotted playing for Aylestone Park and there is a long list of local players who have followed in his footsteps
www.leicestermercury.co.uk