The aim of this study was to determine the effect of age at first calving on first lactation milk yield, lifetime milk yield and lifetime and to determine optimal age at first calving in order to get the highest milk yield in Turkish Holsteins in the Mediterranean Region in Turkey. Data were provided by the Cattle Breeders' Association of Turkey' and included milk yield of Turkish Holstein heifers between 1997 and 2011. A total of 11 097 records of 305 day lactations were analysed according a fixed model, using PROC GLM. In current study, mean first lactation milk yield, age at first calving, lifetime milk yield and lifetime was 5541 kg, 29.81 mo, 9820 kg and 50.63 mo, respectively. The effect of AFC on lifetime milk yield and lifetime were significant (P<0.05) while the effect of AFC on first lactation milk yield was not significant (P>0.05). In conclusion, the determined optimum age at first calving was 23 month for the maximum first lactation milk yield and maximum lifetime milk yield.