If you liked the A Bride's Story manga, the Anime-Planet community thinks you'd like:
In the late 19th Century, England was effectively split into two ‘countries' - that of the aristocratic and rich, and all those below them. One day William Jones, the young son of a rich merchant, pays a visit to his former governess Mrs Stowmar. When he arrives, there is an instant connection between him and Emma, the hard-working and beautiful young maid who works there. After several chance encounters their attraction deepens, but their difference in social status is something which cannot be ignored. With William's father refusing to give his consent to their relationship and intent on arranging a marriage for him with Eleanor, the daughter of a Viscount, there are an increasing number of obstacles standing in their way. In a society where the relationship between a humble maid and a gentleman is forbidden and one is expected to marry within their social rank, can Emma and William's love survive?
Another manga made by Kaoru Mori. It is just as incredibly detailed in the artwork and the historical references used. A must read!
If you liked Emma or A Bride's Story, for it's art, romance or the general style, then you are going to love the other one as well. Both of those were written by the same person, so it's not surpassing that they feel alike.
Both of these manga are written by the same author, and likewase they both are highly realistic portrayals of the time period they are set in; it is painfully obvious that Kaoru Mori had done his research (going above and beyond what the average mangaka or storyteller would) in order to make the characters and the setting as real to the reader as a history book. The art and the relationships between the characters of their respective stories are real and emphatic, and the plot moves ever-forward without feeling rushed. If you like one, I highly recommend the other simply for those qualities.
Dear Mine also has an arranged marriage (engagement to be exact) between a young boy and an older girl and also has a "sweet" feel to it. However that "sweet" feel is achieved in Dear Mine by "fluff & sugar" rather than anything else. On top of that the heroine there is a relatively generic shoujo one (not a strong one like in Otoyome-gatari). There is still some chance that you might like Dear Mine if you liked Otoyome-gatari, so you might as well give it a shot.
When speaking of older female x younger male romance with considerable age gap there are two series that stand out. First is Otoyomegatari which has probably the best take on the subject in seinen manga ever. Second is Kumiko & Shingo which may appear similar to it's shoujo peers, but stands out due to it's length and the fact that the story spans many years.
If you feel like you need middle-eastern setting in your manga than Otoyome-gatari and Shihou Sekai no Ou are series for you. Note that this recommendation is based solely on the setting. If you hope for something with similar story, those series couldn't be further away from each other.
Both series sport an older girl being married to a younger guy and in both series the girl has a little trouble figuring out her relationship with him (due to his young age). The difference is, the duo from Otoyome-gatari get along pretty well, while the main characters from Soredemo Sekai wa Utsukushii don't (at least not on the surface).