Revisit of cosmic age problem
  We investigate the cosmic age problem associated with 9 extremely old
globular clusters in M31 galaxy and 1 very old high-$z$ quasar APM 08279 + 5255
at $z=3.91$. These 9 globular clusters have not been used to study the cosmic
age problem in the previous literature. By evaluating the age of the universe
in the $\Lambda$CDM model with the observational constraints from the SNIa, the
BAO, the CMB, and the independent $H_0$ measurements, we find that the
existence of 5 globular clusters and 1 high-$z$ quasar are in tension (over
2$\sigma$ confidence level) with the current cosmological observations. So if
the age estimates of these objects are correct, the cosmic age puzzle still
remains in the standard cosmology. Moreover, we extend our investigations to
the cases of the interacting dark energy models. It is found that although the
introduction of the interaction between dark sectors can give a larger cosmic
age, the interacting dark energy models still have difficulty to pass the
cosmic age test.
