Do huge age differences really matter in a marriage or relationship?
The Bible doesn’t focus much on age differences. Abraham was ten years older than Sarah was. Many of the Jewish men married girls five to ten years younger than they were, although that was part of their culture, but what about huge age differences of ten years or more? I think the greatest issue with marriage is being unequally yoked in the faith. The Bible teaches we are not to be unequally yoked with non-believers. That certainly includes marriage. That doesn’t mean we cut ourselves off from the world. Jesus prayed for the disciples that while they were still in the world, they would not be of the world (John 17:12). The Apostle Paul wrote, “Do not be unequally yoked with unbelievers. For what partnership has righteousness with lawlessness? Or what fellowship has light with darkness” (1 Cor 6:14). Maybe Paul had in mind the Old Testament law that said, “You shall not plow with an ox and a donkey together” (Deut 22:10). Why was that a law? Because the ox may want to go one way while the donkey decides to go another…or just sit! Then, the ox does all the work! That’s not an equally yoked team. So too is a believer and non-believer when yoked or joined in marriage. One will pursue the things of the world and try to go one way, while the other seeks the things of God and tries to go another. One will pull or drag on the other, especially if they’re going in different directions, but they will not be working together as a team. That’s a problem. God did not want us to marry unbelievers just as ancient Israel was forbidden to marry pagans. God knew they’d quickly adopt the ways of the pagans and stop worshiping God. In an unequally yoked marriage, one may eventually cease from worshiping God at all. Even if they don’t, the journey’s going to be very difficult, because the man and the woman are not going to be going the same direction, nor will they be pulling with the same force. 
Water and Oil
I remember my old car was finished when I found oil in the water. The block was cracked and some of the engine oil found its way into my radiator, but I noticed the water and oil didn’t mix. I have found from experience that light and darkness don’t mix either. The light overcomes the darkness, but the darkness cannot overcome the light, particularly the Light of the World, Jesus Christ (John 1:4). We were called out of the darkness and into the Light, and now we’re charged to bring the Light into the darkness so we can bring others out into the Light, but that doesn’t mean we join the darkness. For one thing, our “bodies are members of Christ” (1 Cor 6:15), and members of Christ’s body don’t do well when joined with body members of the world. Jesus said there are only two kinds of children in this world; the children of darkness, or of the Devil, and the children of the God, or those for who trust in Christ. The Jews claimed Abraham as their father, but Jesus told them, “You are of your father the devil, and your will is to do your father’s desires. He was a murderer from the beginning, and does not stand in the truth, because there is no truth in him. When he lies, he speaks out of his own character, for he is a liar and the father of lies” (John 8:44). The Apostle John says that “we are God’s children now, and what we will be has not yet appeared; but we know that when he appears we shall be like him, because we shall see him as he is” (1 John 3:2), so there are only the children of the Devil and the children of God. These children should never intermarry. That much is clear from Scripture.
As I wrote before, age differences are not a huge factor in marital success; being unequally yoked is. It’s a different story when you’re talking about someone who got saved after they were already married, but even that is God’s will. God may use the Christian spouse as a means to lead their mate to Christ (1 Cor 7:16), but the greatest sin in marrying someone is not the age difference, but whether they both agree that Jesus is their Savior. Problems do arise when one spouse is much older than the other because, as the years pass, one spouse will begin to slow down a bit and not enjoy the things they used to enjoy, or they won’t be able to do the things they used to do. This includes certain sporting events, carnival rides, eating certain foods, or anything that requires a lot of endurance. Then there are the generational differences, like tastes in music, clothing style, movies, and even differences in raising children, and the greater the age difference, the greater chance that these will become significant issues. Still, these differences can be overcome by the Spirit of God because we are all joined together in one Body, Jesus Christ, and we all have the same Father and access to the same Spirit.
If the age differences already bother one spouse or the other, then there could already be trouble in paradise. These things should be ironed out in Christian marriage counseling well in advance. Statistics prove that marriages have fewer divorces when they are equally yoked in the faith, but also when they receive premarital counseling. There’s certainly wisdom in godly counsel. There are things the counselor might see or think about that neither one of the couple even thought about. Where will they live…in the city or country…what about children? What disciplinary methods do they believe in? These questions need to be asked before moving on with the wedding plans, but long before that, both must be in agreement about their faith in Jesus Christ. A house divided won’t stand very well, even with a Christian spouse in it. A spiritually divided house is not what God intended. It wasn’t that way in the beginning, and I believe it shouldn’t be that way now.
Here is some related reading for you: 7 Ways to Make Your Marriage Better 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.