Because Shelke hasn't had a childhood or a teenage years, shes been locked down in deep ground no chance to experience a normal life and if we consider Shelke to be 19 then the same logic must apply to Vincent make him 60. Its not just a simple as saying shes actually 19, shes been basically switched off for 9 years just as Vincent was for 30 years, the situation is complicated but i think if we use differen't logic for each character then it loses all sense completely.