We use large-scale molecular dynamics simulations to study aging of the velocity autocorrelation function of a force-free granular gas consisting of viscoelastic particles. We study the velocity autocorrelation function for a simplified model where the coefficient of restitution is constant for all collisions, but depends on current temperature of granular gas, it is called quasi-constant coefficient of restitution epsilon(eff). From our simulation results, it is observed that A(tau(tw), tau) depends independently on both tau and tau(w). Initially, A(tau(w), tau) decays exponentially but later as tw increases, A(tau(w), tau) decays slowly due to emergence of correlations in velocity field. The explicit dependence of A(tau(w), tau) on tw implies that the system exhibits aging property.