A Ginzburg criterion is employed to estimate the extent of the critical region for the restricted primitive model (RPM) of an ionic fluid. Mean-field critical amplitudes are calculated using the generalized mean-spherical approximation (GMSA) and other recently proposed theories. The resulting (reduced) Ginzburg temperature tG is large and similar to that calculated for models of a one-component neutral fluid. This implies that crossover from mean-field to Ising-like critical exponents should not be expected for the RPM. The relevance of these results for the criticality of real ionic fluids is discussed.