We present the Kepler photometric light-variation analysis of the late-type double-lined binary system V568 Lyr that is in the field of the high metallicity old open cluster NGC 6791. The radial velocity and the high-quality short-cadence light curve of the system are analysed simultaneously. The masses, radii and luminosities of the component stars are $M_1 = 1.0886pm0.0031, M{odot}$, $M_2 = 0.8292 pm 0.0026, M{odot}$, $R_1 = 1.4203pm 0.0058, R{odot}$, $R_2 = 0.7997 pm 0.0015, R{odot}$, $L_1 = 1.85pm 0.15, L{odot}$, $L_2 = 0.292 pm 0.018, L{odot}$ and their separation is $a = 31.060 pm 0.002, R{odot}$. The distance to NGC 6791 is determined to be $4.260pm 0.290,$kpc by analysis of this binary system. We fit the components of this well-detached binary system with evolution models made with the Cambridge STARS and TWIN codes to test low-mass binary star evolution. We find a good fit with a metallicity of $Z = 0.04$ and an age of $7.704,$Gyr. The standard tidal dissipation, included in TWIN is insufficient to arrive at the observed circular orbit unless it formed rather circular to begin with.
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