def METHOD_NAME(field,data):
    ad = data.ds.all_data()
    if data.ds.cosmological_simulation == False:
        #we assume that the romeel stellar ages are the same as
        #normal gadget for idealized simulations, but in yr.  but
        #this could be totally wrong. 
        simtime = data.ds.current_time.in_units('yr')
        simtime = simtime.value
        age = simtime-ad[("starformationtime")].value #yr (assumes that ad["starformationtime"] is in Myr for benopp/romeel Gadget)
        #make the minimum age 1 million years 
        age[np.where(age < 1.e6)[0]] = 1.e6
        print ('\n--------------')
        print ('[SED_gen/star_list_gen: ] Idealized Galaxy Simulation Assumed: Simulation time is (Gyr): ',simtime)
        print ('--------------\n')
    else:
        simtime = data.ds.current_time.in_units('Gyr')
        simtime = simtime.value
        age = ad["starformationtime"].value #yr
        #make the minimum age 1 million years 
        if len(np.where(age < 1.e6)[0]) > 0:
            age[np.where(age < 1.e6)[0]] = 1.e6
        print ('\n--------------')
        print ('[SED_gen/star_list_gen: ] Cosmological Galaxy Simulation Assumed: Current age of Universe is (Assuming Planck13 Cosmology) is (Gyr): ',simtime)
        print ('--------------\n')
    age = data.ds.arr(age,'yr')
    age = age.in_units('Gyr')
    return age