Context. The typical uncertainties of ages determined for single star giants from isochrone fitting using single-epoch spectroscopy and photometry without any additional constraints are 30–50%. Binary systems, particularly double-lined spectroscopic binaries, provide an opportunity to study the intricacies of internal stellar physics and better determine stellar parameters, particularly stellar age. Aims. By using the constraints from binarity and asteroseismology, we aim to obtain precise age and stellar parameters for the red giant-subgiant binary system KIC 9163796, a system with a mass ratio of 1.015 but distinctly different positions in the Hertzsprung–Russell diagram. Methods. We computed a multidimensional model grid of individual stellar models. From different combinations of figures of merit, we used the constraints drawn from binarity, spectroscopy, and asteroseismology to determine the stellar mass, chemical composition, and age of KIC 9163796. Results. Our combined-modeling approach leads to an age estimation of the binary system KIC 9163796 of 2.44‑0.20+0.25 Gyr, which corresponds to a relative error in the age of 9%. Furthermore, we found both components exhibit an equal initial helium abundance of 0.27 to 0.30, which is significantly higher than the primordial helium abundance, and an initial heavy metal abundance below the spectroscopic value. The masses from our models are in agreement with the masses derived from the asteroseismic scaling relations. Conclusions. By exploiting the distinct positions of the components of KIC 9163796, we successfully demonstrate that combining asteroseismic and binary constraints leads to a significant improvement in the precision of age estimation, resulting in a relative error in age below 10% for a giant star.