Martin, in quoting from this passage on p. 125 of The Story of Dartmouth , has "gentlemen" instead of "gentleman."

The MS appears to favour the singular. Even so, it is possible that Louisa intended the plural; for on another occasion (14 Nov.), when she very clearly intends the plural, it appears she has written the singular form "gentleman."

If she intended the plural here, that plural can be understood in two ways: to refer to all or most of the young gentlemen attending the ball--as having undertaken to host it together; or to refer to the two young men that apparently live at Mount Edward: William Allen Jr., aged 20 (see O13n1-3 ), and his younger brother Alexander, aged 17 See N12n5 .

If she intended the singular--which would seem to accord with the more usual, the more traditional way of hosting a ball (if classics like "Cinderella" are any touchstone)--then it would seem she is talking about William Allen Jr. Of him little is known. He walked Louisa and Charlotte home on a beautiful October moonlit night. He may have visited Colin Grove shortly afterwards, on 19 and 29 Oct. And he may be hosting the ball at Mount Edward this evening. But if he is the young gentleman host of the ball, what happens to him subsequently is not in keeping with the fairy tale's happy ending. William Allen died just three months later, on 4 March 1816--six months before his 21st birthday.