By adopting the recently empirically derived dependence of {alpha}-elements on [alpha/Fe] instead of the conventionally applied uniform one, we tested the agreement between stellar model predictions and observations for RGB stars in the APO-K2 catalogue. We particularly focused on the biases in effective temperature scales and on the robustness of age estimations. A slight {DELTA}T difference of 25K was detected between stars with high and low {alpha}-enhancement. A multivariate analysis reveals a dependence of {DELTA}T on both [Fe/H] and [{alpha}/Fe], and highlights a significant dependence on stellar mass. Despite differences in assumed chemical composition, our analysis, through a fortunate cancellation effect, yields ages that are largely consistent with recent studies of the same sample. Notably, our analysis identifies a 6% fraction of stars younger than 4 Ga within the high-{alpha} population. However, our analysis of the [C/N] ratio supports the possible origin of the these stars as a result of mergers or mass transfer events.