Some people dislike interracial marriages, but these marriages happen anyway.
The same people often dislike same-sex marriage, but it is spreading around the world.
Some people also oppose inter-religion marriage. In certain cultures, the punishment is death.
I am interested in the common dislike of May-December romances. Like that of singer Mick Jagger, age 73, and partner Melanie Hamrick, age 29.
Then there is tycoon Rupert Murdoch, age 85, and Mick Jagger’s former wife, Jerry Hall, age 59.
May-December couples are so interesting that there is even a show on Netflix called Age Gap Love.
Some of the couples violate norms more than others by involving a woman who is much older than the man.
These romances face gale-force social headwinds.
Critics of big age gaps in romance believe the relationships are abnormal, exploitive and doomed to failure.
The relationships certainly are abnormal in the sense of being rare.
Most individuals marry someone about their own age. In male-female couples, the man is usually a few years older.
I am not sure who is exploiting whom in the Mick Jagger relationship. Maybe neither of the two partners is under the thumb of the other.
Studies show divorce is much more likely in married couples with an age gap of at least 20 years. That is something to consider.
I believe in live and let live, so as far as I am concerned adults can pair off with just about anyone they want.
But I absolutely draw a line with regard to children.
I would not approve of a marriage with one partner under 17.
So I would rule out February-December relationships.
I also would not approve of a romance between first cousins.
Risks of genetic disorders are higher in closely related individuals.
But I am open to further evidence on the subject.
Of course, no-one is asking for my approval, not even my own children.
So I could keep my opinion to myself, but where is the fun in that?
What are your views about appropriate couplings?
John Malouff is an Associate Professor at the School of Behavioural, Cognitive and Social Sciences, University of New England.
