Bella Heathcote was 20 in Acolytes when she played the character 'Petra'.
That was over 15 years ago in 2009.
This was her first recorded movie acting credit (although may not technically be her first actual acting role).
Today she is 36, and has starred in 14 movies in total, 13 of those since Acolytes was released.
In Acolytes, I think Bella Heathcote looks: