AgeRefPlot min/max when choosing a subset

[TalShor]

because of this default:
age_bins = np.arange(35, 75, 1)
even if you're data is not between 30-80 (subset, different, whatever) - it'll still show 30-80

set the default more data aware

[TalShor]

Also the param expectiles is not optional - None or False will throw an exception