I think that it would be more natural to say 'He's a sporty boy', or 'He's quite sporty'. Please be aware though that Chinese people tend to overuse 'boy'. I would only say that of someone that is younger than around 13. Here in New Zealand we use the term 'the boys' to refer t to groups of boys or men, but we would definitely not use 'a boy' to refer to someone (say) 20. 'Young man' would be more appropriate there, or