My husband is 5 months younger. I think it's best to marry someone roughly your own age for two reasons.
1. Retirement benefits come at the same time. An acquaintance's 3rd husband is 8 years her junior. She was a bit show-offy about it for a few years - her younger man. Then he was laid off during a downsizing at age 50 and has been unable to find another job. He's now 59 and she's 67, but she can't retire because they need the income and he needs the medical benefits. Their marriage appears happy and solid, but I'm sure she's thinking it would have worked out better if they were the same age.
2. You experience cultural events in roughly the same way. About 30 years ago we were at a party chatting about how we'd each experienced the night the Beatles were first on Ed Sullivan. One told of not being allowed to watch, but she nevertheless knew all about it and had been swept up in the excitement of Beatlemania and the English Invasion. Another friend told of how he and his older brothers watched together. We turned to his wife next. She said, "I was two." (She was ten years younger than her husband.) We moved on to the next person, but that moment stuck with me to this day.