In my latest book (A Proposal of Marriage) some readers had a difficult time accepting the significant age difference in my 20-year-old heroine and the 43-year-old man she marries. I know when I was 20 I would have thought a man even just ten years my senior far too old. But let us not judge Regency-era characters by today’s standards.
Not just in England, the country in which I set my books, but also in the United States during the 1800s those May-December weddings were far more common. Some have speculated the reason for this may have to do with younger men in those days having fewer financial options and having to wait until they inherited before they were in a position to wed.
As a student of Regency England, I can point to several actual marriages among the upper classes in which there were significant age differences. All but one of them was a successful marriage.
The one that was not as successful was that between the former Emma Hart and the English ambassador to Naples, Sir William Hamilton. The marriage between Lady Hamilton and Sir William was successful—until the naval hero Lord Horatio Nelson entered her sphere and became her lover. Sir William was 28 years older than his wife. Her lover was just seven years her senior. The two lovers carried on their affair right under the nose of her cuckold husband—even through her “secret” pregnancy of Lord Nelson’s illegitimate child.
Lady Harriett Cavendish, the daughter of the Georgiana, Duchess of Devonshire, married her aunt’s lover, Granville Leveson Gower, a man 12 years her senior. It was a solid marriage, during which Harriett adored her husband, who became the ambassador to France.
A similar age difference, a 13-year gap, distinguished the marriage of the 1st Viscount Palmerson (father to the future Prime Minister) and his second wife and mother of his children. (His first wife had died on childbed, along with their only babe.)
Harriett Fane, one of 14 children born to a younger son of the Earl of Westmoreland, found security when she married Charles Arbuthnot, a man 26 years older than her. Her husband not only was a member of Parliament, but he was also close friends to the hero of Waterloo, the Duke of Wellington, a man who was completely smitten over Mrs. Arbuthnot, though there’s no evidence of an actual affair between the two. She did serve as his hostess—and a buffer against the large number of women who threw themselves at this hero, who also served twice as Prime Minister. When Mrs. Arbuthnot died suddenly at age 40, both men (both easily old enough to be her father) grievously mourned her and lived together the rest of their lives.
And the largest age gap I’m going to write about today is the 32-year-old gap between the wealthy banker to the ton, Thomas Coutts, and the actress Harriett Melon. She seemed most fond of her husband and was close to his grown daughters by his deceased first wife.
Remember, in many cases young men in their twenties during the early part of the nineteenth century did not have the financial resources in which to offer for a wife. If she wanted home and family, she was often better off marrying an older man.
Cheryl Bolen's Regency Ramblings 
I’ve always found older men attractive; in fact I worried if my husband was a bit young when I fell in love and married him, I was 17, he was 25, and I always have felt the older one of the two of us. We’ll have been married 38 years come January. Older men have a stability to them, as well as the financial considerations involved.
I can’t say a word, given that my husband was twenty years older.