The reference to this question can be found in Chapter Four. We are not actually given the name of the elderly man that offered to marry Kit back in Barbados. We are merely told the following information concerning him when Kit shares the story with Mercy and talks about this man:
He used to come often, and afterwards I found he had lent Grandfather money, hundreds of pounds. He didn't want the money back--he wanted me to marry him. He tried to make me think that Grandfather had wanted it, but I'm sure that was not so... He was very kind. But Mercy, he was fifty years old, and he had pudgy red fingers with too many rings on them.
Although we do not know his name, we can see that he clearly had Kit in a powerless position, and tried to use the power that he had over her to force her into a marriage with him. Although he was "very kind," according to Kit, the way in which he tried to make Kit believe that her grandfather would have wanted them to be married suggests a somewhat darker side to his personality. He is never mentioned again in the book.