  Standard stellar evolution theory poorly predicts the surface abundances of
chemical species in low-mass, red giant branch (RGB) stars. Observations show
an enhancement of p-p chain and CNO cycle products in red giant envelopes,
which suggests the existence of non-canonical mixing that brings interior
burning products to the surface of these stars. The 12C/13C ratio is a highly
sensitive abundance metric used to probe this mixing. We investigate extra RGB
mixing by examining (1) how 12C/13C is altered along the RGB and (2) how
12C/13C changes for stars of varying age and mass. Our sample consists of 43
red giants spread over 15 open clusters from the Sloan Digital Sky Survey's
APOGEE DR17 that have reliable 12C/13C ratios derived from their APOGEE
spectra. We vetted these 12C/13C ratios and compared them as a function of
evolution and age/mass to the standard mixing model of stellar evolution and to
a model that includes prescriptions for RGB thermohaline mixing and stellar
rotation. We find that the observations deviate from standard mixing models,
implying the need for extra mixing. Additionally, some of the abundance
patterns depart from the thermohaline model, and it is unclear whether these
differences are due to incomplete observations, issues inherent to the model,
our assumption of the cause of extra mixing, or any combination of these
factors. Nevertheless, the surface abundances across our age/mass range clearly
deviate from the standard model, agreeing with the notion of a universal
mechanism for RGB extra mixing in low-mass stars.
