Question: "What does the Bible say about age differences in relationships?"
Answer: The Bible very rarely gives us age examples in marriage relationships (or in any other situation for that matter). We do know that Abraham was 10 years older than Sarah (Genesis 17:17), but there are no other couples in the Bible where both individuals’ ages are given. It is often assumed, for example, that Joseph was significantly older than Mary. However, there is absolutely nothing in the Bible that indicates this.
Age can be important in a marriage, but it is far less important than other issues such as salvation, spiritual maturity, compatibility, etc. As people get older, age difference means less and less. Obviously, a 40-year-old marrying a 20-year-old will be questioned while no one will think twice about an 80-year-old marrying a 60-year-old. The only warning regarding age in marriage is to avoid marrying someone young for lustful purposes, and avoid marrying someone older for money. The best course of action is to pray to God for wisdom concerning any prospective relationship (James 1:5).