Younger women can be interesting to older men because they make them feel young again. They get to have a sort of second chance at all the things they did wrong in their earlier relationships. They get to feel mature, knowledgeable, worldly, but still have fun. Younger women have not yet settled down to a comfortable dull life.
Older men can be interesting to younger women because they are more mature, more caring, typically have a higher opinion of women than younger men do. Older men are typically wealthier, able to do more interesting things.
The down side is that people of different ages do think rather differently, care about different things. There is a natural power imbalance in this sort of relationship, the women is sort of lover and child at the same time. Later in life the older person becomes elderly and feeble early, leaving the younger person to care for them.
My personal opinion is that relationships with a big age difference are fine if both are in it for short to medium term fun, but not if either wants a lifelong relationship.