I know a story where the sister was one year younger than the brother; he was 24, she was 23.
She asked if she could date, and he said yes.
So she dated several times and then was ready to get engaged.
She asked if she could get engaged, and he said no.
His excuse was that he didn’t like the guy she was dating and thought it wasn’t a good idea.
Now, he is married with several children, while she is still single.