Whenever a decadeslong marriage ends, it is shocking because people assume that after that many years, a couple is set for life. That isn't necessarily true. Splitting later in life is becoming more and more common. These divorces don't happen on a whim or spur of the moment; usually the underlying factors have been building for years.
For example, age differences, while not pronounced when couples are young, can become an issue as they age. An author of a book on relationships asserts that as people grow older they go through "brain upgrades" at certain points in their lives. This shifts the way they think and approach the world. So that 15 year age difference, which did not matter when they were younger, can contribute to a breakdown in communication as they grow older.
The author also points out that over time communication can break down as a couple tends to "grow apart" from one another. This is the proverbial death by a thousand paper-cuts to the marriage. No single thing necessarily ends a marriage; it is a series of small decisions that led the couples to not take their commitments seriously. Over time this creates cracks in the relationship that eventually causes it to shatter.
Another major issue, according to the writer of a book dealing with sexual relations, is that hormonal changes can result in sexual incompatibility. Every person experiences these changes differently but reduced sex drive can put significant stress on a relationship.
Additionally, a mental toughness coach says that couples, especially retired ones, are around each other all day every day. This can lead to boredom as couples begin to take one another for granted. This isn't a single decision but rather an accumulated series of decisions that results in complacency in the relationship.
If you are considering divorce, especially if you are retired, then it is advisable you consult with an attorney. Dividing up your retirement and investment assets is a complicated endeavor that an attorney can smooth out. Divorce is a big decision for all couples. Don't risk your retirement or livelihood by not taking this seriously.
Source: The Huffington Post, "The 5 Big Reasons Why Couples Divorce After Decades Of Marriage," Linda Melone, Mar. 20, 2016