Having sex with someone you are not married to (YET) is premarital sex whether you are 15 or 115.
Of course I did. It is Pornia.
In the regular Greek society that meant all kinds of sexual activities. In the Greek speaking Jewish diaspora it included anything that violated the sexual ethics of the Old testament. And that included all kinds of non-marital sex.
Of course He did. Matt 15.19 is Him speaking about pornia.
Correct. You need to understand the definitions of the original language - in this case Koine Greek.
He said "If you love me you will keep my commandments." Jn 14.15 And since God is one, all the OT commands are His commandments.
1 - much of the so-called "Christian understanding" is wrong.
2 - to my knowledge of the so-called "Christian understanding," anything between husband and wife is ok; including frequency of 3x a day to 3x a decade.
Go to a seminary and find out the local background of what was going on in Corinth to warrant Paul's affirmation.
Because the so-called "Christian understanding" of the term modesty is strictly sexual. In modern times that is a judgement on how much female skin is showing. But that is NOT what any of the NT authors meant. It was about not flaunting wealth.
It contradicts what some people THINK the "Law of Love" is. And to understand Paul, you have to understand that he was taking the OT teachings and giving them application in the NT. He also had additional divine revelation on how Gentiles were to fit into the Redeemed people of God without formally converting to Judaism. (but that a topic for another discussion)
If you see our Lord and Paul as being in contradiction, you have one or both of them in the wrong light.