But it doesn't fail all the time.
I think this is a case-by-case thing, and that hard and fast rules do not apply to everyone equally.
A book really needs to be written on this subject. Here's a chapter that I'll begin with.
Everyone has differences and there are many options. There are only a few laws God gives about marriage .
I was asked by a mutual friend to help him move furniture for a married couple he was friends with. My buddy and I had a business hauling heavy things and were used to that. No problem, I had a Saturday available and we all need a hand at times.
They had a double wide and a little piece of land way out in the country. She was employed in some technical role for NASA, high IQ, into the book of the week club, extremely pretty and healthy. There was something like a 50+/- year age gap. He was and also smart and able. He just needed help moving some big items into storage.
After that day, we connected with them on occasions at lunches at mutual educational and Bible conferences. I doubt if either one of them could care less what others thought about that little detail of their marriage. We thought they were pretty cool.. They weren't worried about opinions like some 14 year olds.
Were they living in sin? I couldn't find anything in the Bible that said two adults, male and female I should add, must marry at a certain age range. That's a choice, not a sin, or something addressed as our youth obsessed culture demands. On the other hand, it seems that worldly minded youth has no problem with the things God really cares about . Living in sin..... promiscuity......drugs and alcohol...... rebellion to the established boundaries that God has provided.....etc.
Then the weak minded culture looks to the youth as something to desire to make one happy, like some fruit on a tree of knowledge. They can have their warped sense of reality and immaturity. It's of the world, the flesh and the devil.
Christians can find enjoyment in everything God has provided within His Word. That's a lot and it doesn't carry the baggage of addictions or consequences.
Back to the conclusion about the couple that I knew. They were not Christians, but were active and pursued meaningful growth in areas of interest. They seemed very happy and met their needs without government assistance. They didn't even use the health care benefits.
The man had something that the wife thought he should have checked out.by a doctor. That turned out to be a mistake. He never needed medical care before and was not on any meds either. They were both healthy. Unfortunately, the hospital took care of that and his life was cut short. Many worry so much about widowhood. Well, the wife stayed single and died shortly thereafter even though she was yet a good bit younger. She died after a car accident. People usually have no idea when that day will come. With her, she was given just one year from the week we last spoke about the Lord.