I did say 'historically' i.e. that it's no longer the case and governments have gradually been trying to create equality between the sexes over retirement age.

Is it the law or only preference that men work longer?

It was the law that men only received the state pension at 65, that's where the unfairness lay, but yes, in the unlikely event they were well enough off they could retire earlier but not receive any pension.

I'm sure today many women in the UK are the main breadwinners in the household, and many times the only breadwinner.