These factors would reduce the risk of divorce because they would allow the couple to be more mature and less stressed.
A couple that marries when they are both older than 25 is a couple that is more likely to be mature. The partners will be less likely to be rushing in to a marriage. They are more likely to know what sort of a person is good for them. They are more likely to be grown up enough to work out their marital problems when such problems occur. All of these factors make them less likely to get divorced.
When marriages do break up, they often do so because of stresses in the lives of the partners. When people are stressed, they are harder to get along with. They may not have the time or the inclination to do things with their partners that will help to build and maintain the relationship. An annual income under $25,000 is very low. Partners who have such a low income for any significant length of time will endure a great deal of financial stress. This is more likely to cause them to get divorced.