Ages of extragalactic globular clusters can provide valuable insights into the formation and evolution of galaxies .
In this contribution the photometric methods of age dating old globular cluster systems are summarised .
The spectroscopic approach is reviewed with an emphasis of the right choice of age diagnostics .
We present a new method of quantifying the relatively best age-sensitive spectroscopic index given the quality of a data set and a certain theoretical stellar synthesis model .
The relatively best diagnostic plot is constructed from the set of Lick indices and used to age date globular clusters in several early-type galaxies which are part of a large spectroscopic survey of extragalactic globular cluster systems .
We find that , independently of host galaxy , metal-poor ( [ Fe/H ] < -0.8 ) globular clusters appear to be old ( t > 8 Gyr ) and coeval .
Metal-rich clusters show a wide range of ages from \sim 15 down to a few Gyr .