Old people take exercise classes all the time, from tai chi, aqua fit, zumba and yoga at my gym. Doctors encourage it and some insurances even cover it as preventive health care. So what if it's ballet? He is a grown adult and he's the one paying for it. Why the drama? Maybe to an old person in Japan a western dance is seen as something only little girls take? Japan is strangely progressive and old fashioned at once. Even after half my life reading and watching Japanese books and shows I still find their culture complex and confusing.
Edit: in which I realize this is Korean and have no idea what I'm talking about. ... *face palm*