Distribution of the mass-weighted ages for sample galaxies in different types. The green, red, and blue lines represent the samples of BCGs, MGs, and FGs, respectively. The thin dotted lines represents the age distribution obtained for LRGs with velocity dispersion > 210 km s^-1 by the full spectrum fitting in this paper, and the thick solid lines represent the age distributions obtained from a semi-analytic galaxy formation model (Guo et al. 2011). Some SDSS LRGs appear to have ages or lookback times of 15 Gyr, larger than the Hubble time, because of measurement errors in the STARLIGHT-derived ages.