'Age of the universe in Gyr at redshift ``z``.
Parameters
z : array-like
Input redshifts.  Must be 1D or scalar.
Returns
t : `~astropy.units.Quantity`
The age of the universe in Gyr at each input redshift.
See Also
z_at_value : Find the redshift corresponding to an age.'

def age(self, z):

    from scipy.integrate import quad
    f = (lambda red: quad(self._lookback_time_integrand_scalar, red, np.inf)[0])
    return (self._hubble_time * vectorize_if_needed(f, z))
