  Stellar spin down is a critical yet poorly understood component of stellar
evolution. In particular, results from the Kepler Mission imply that mature
age, solar-type stars have inefficient magnetic braking, resulting in a stalled
spin down rate. However, a large number of precise asteroseismic ages are
needed for mature ($\geq$ 3Gyr) stars in order to probe the regime where
traditional and stalled spin-down models differ. In this paper, we present a
new asteroseismic benchmark star for gyrochronology discovered using
reprocessed Kepler short cadence data. KIC 11029516 (Papayu) is a bright
($K_{p}$ = 9.6 mag) solar-type star with well-measured rotation period
(21.1$\pm$0.8 days) from spot modulation using 4 years of Kepler long cadence
data. We combine asteroseismology and spectroscopy to obtain
$T_{eff}=5888\pm100$ K, $\rm{[Fe/H]} = 0.30 \pm 0.06\,$ dex, $M = 1.24 \pm 0.05
M_{\odot}$, $R = 1.34 \pm 0.02 R_{\odot}$ and age of 4.0 $\pm$ 0.4 Gyr, making
Papayu one of the most similar stars to the Sun in terms of temperature and
radius with an asteroseismic age and a rotation period measured from spot
modulation. We find that Papayu sits at the transition of where traditional and
weakened spin-down models diverge. A comparison with stars of similar zero-age
main-sequence temperatures supports previous findings that weakened spin-down
models are required to explain the ages and rotation periods of old solar-type
stars.
