An Afghan-born teenager accused of sexually assaulting eight young females in surf at a Gold Coast beach claims he is 16, not 18, and should be tried as a child.

The Victorian-based teenager, facing 13 charges, including multiple attempted rape and sexual assault offences, allegedly committed the attacks at Surfers Paradise about midday on January 12.

A teenager has been accused of sexually assaulting eight young women in the water at Surfers Paradise. Credit:Glenn Hunt

His lawyer told the Southport Magistrates Court during a brief mention of the case on Thursday that his client says he is 16, not 18, and shouldn't be tried as an adult.

The teen and his family claim the accused arrived into Australia as a boy without official documents and was given an older age than he actually was by immigration officials.