In my opinion, the age of consent should be linked to physical maturity and not an artificial age of consent age such as 16 or 18 (in one state it is actually 14). Physical maturity means the ability to conceive a child. When a child turns into a physically mature adult, she could elect to go on birth control to avoid getting pregnant if the family decided it would be a bad idea to start having children at such a young age.
When Mother Nature releases the hormones that turn individuals into physical adults, the sex drive is usually a stronger force than any written laws that create an artificial age of consent (no matter the punishment), which ignores the influence of God, DNA, genetics, hormones and/or Mother Nature (depending on what one believes).
If God had wanted children to stay children until the age of 14, 16, or 18 (depending on the state), He would have made sure those children's physical maturity obeyed the artificial laws written by men that ignore the reality He created. Hmm, imagine a 16 year old living in a state where 16 was the age of consent and then moving to California where it is 18. God would have to flip off the hormones and revert that young adult back into a child to obey man's artificial laws.
However, since society frowns on relationships between teens and someone decades older (evidently God and Mother Nature do not frown on it since physical maturity can arrive at anytime between 12 and 16 — on average — when I was teaching I knew of a young girl that was age 9 that got pregnant so there are exceptions to the average), then possibly the law could define what is legal between individuals by the number of years in age.
For example: If it were legal for a 13 year old that was sexually mature to have sexual partners, then the law might stipulate that anyone more than five years his or her age would be breaking the law (this is a suggestion. It could be two years or three years, etc), which means a nineteen year old would go to jail if he or she had consensual sex with a physically mature 13 year old but anyone 18 or younger would not. When that 13 year old turned 14, the five year gap for consensual physical relationships would move up a notch, etc.
At 17, that means he or she would be able to have a legal relationship with someone that is 22 but not 23. In addition, if a fourteen year old was still not physically mature and incapable of conceiving a child, then sex with anyone of any age would be considered illegal, which means if there were twins and one twin became physically mature at 14 and the other one didn't until 16, then the 14 year old could date but the other twin couldn't.
The only reason I suggest this is because so many in America do not approve of young adults having mature relationships with much older individuals.
Since 18 is the age when young people may join the military without parental consent and go to war and die for his or her country, which I did soon after graduating from high school (but I didn't die), then at 18, the age of consent laws should cease to exist and if an 18 year old wants to have a consensual relationship with someone that is 70 or 80 or 90, that is their business. However, to be honest, my wife and I would hate it if our 20-year-old daughter decided to date someone that old, but it is her life—I'm sure we would express our opinions though.
The laws the way that are written today create a conundrum. When I was still teaching, I knew of one young man that broke up with his girlfriend when he turned 18, and she was still 16. They were together for three years and were great together. It was obvious they loved each other.
However, even though this couple had been sexually active and had a strong bond, after his 18th birthday, he feared that he might end up in jail for twenty or more years, so he broke up with her (it was emotional for weeks because they were both in one of my classes), and they were only two years apart. Eventually, they asked me to see if it was possible for one of them to be transferred into one of my other classes so they would not be together.