We argue that the systematic deviation from perfect aging (which means that the relaxation function only depend on the ratio t/tw, where tw is the waiting time) observed in spin-glasses can be accounted for if the number of available metastable states is finite. A significant fraction of these metastable states will be visited after an "ergodic" time which we estimate from the experiments to be ≈ 106 seconds. This corresponds to ≈ 1012-1014 diffèrent metastable states per independent subsystem