We study the decays of the thermoremanent magnetization in Y0.90Na0.10MnO3 for different waiting times at the measuring temperature 33K, well below the spin glass (SG) transition temperature 42K. The results demonstrate that almost perfect full aging can appear even in the case of the cooling time as long as 700s from 60K to 33 K.By subtracting the stationary component A(τ0/t)a (A is a dimensionless constant, t represents the time, τ0 is the microscopic spin flipping time, and α is a parameter always in the rang of 0.1-0.01), the value ofα is found to be much smaller than that reported in other SG systems, which is well consistent with the behaviour of the ac susceptibility. All of them are discussed based on the intrinsic geometric magnetic frustration for the present system.