Even most who have a very limited knowledge of the Bible are aware of the three dispensations laid out in the scriptures, And with these three were three different laws given for God's people. But there is considerable confusion as to who was subject to these three laws and when.
There should be no such confusion because the answers are quite clear when each are studied in the proper context. Let us try and divide aright those places where they confusion develops.
First of all the original law, given directly from God to the heads (patriarchs) of households and is identified as the Patriarchal Law. The entire law is not fully recorded, and in fact, very little of it was recorded. At the time it was given, there were no methods of recording words except inside the hearts of men. No writing, or reading, had been taught or learned. So God simply instructed the original patriarchs as to their duties and laws towards Him. Then they were obligated to pass these laws to their progeny.
While Adam and Eve were in the Garden of Eden they were given very little instructions. The only instructions recorded are located in verses in Genesis second chapter, thus:
"And the LORD God took the man, and put him into the garden of Eden to dress it and to keep it. And the LORD God commanded the man, saying, Of every tree of the garden thou mayest freely eat: But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die." (Genesis 2:15-17 KJV)
And, although their further instructions are not specified when they were put out of the garden, we can find evidence of other things that were commanded of them. We learn soon that they were required to offer sacrifices to God. In the first five verses of chapter 4, the account of the two firstborn sons of Adam and Eve described and we can determine those things which God had commanded. Read Genesis 4:1-5. and you can determine that God
had instructed them to offer an animal sacrifice since he was pleased with Abel's offering and was not pleased with Cain's offering of vegetables.
Little else is listed as plainly as these but we know that they sinned when they took another's life, and much later we learn that the entire populace other than Noah and his family, had become evil and were committing a number of sins including adultery and other evils. Read the first 8 verses of Genesis 6 and you will see several things which were very displeasing to God so it is safe to assume that the people had been instructed not to do these things.
Even after the flood and the earth was cleansed of those sinful people, sin again increased as did the population. By the time of Abraham, the world was mostly wicked and were leaving God our of their lives. Abraham himself was raised a midst idol worshipers, and in fact, Joshua after they had taken the Canaan land implicated Abraham's father Terah, read this:
"And Joshua said unto all the people, Thus saith the LORD God of Israel, Your fathers dwelt on the other side of the flood in old time, even Terah, the father of Abraham, and the father of Nachor: and they served other gods." (Joshua 24:2 KJV)
But even after being raised under these circumstances, Abraham remained faithful to God and was chosen to be the father of God's chosen people to furnish the lineage to Jesus Christ. The Israelites.
When reading the accounts of the various peoples then inhabiting the earth, it appears that virtually all had again chosen to worship false gods. But after God promised Abraham that his seed would be a people set apart from the rest of the world and this people would be the descendants of Abraham, Isaac and Jacob. Jacob then, after being renamed 'Israel', produced 12 sons which would become the 12 tribes of Israel and were later referred to as Jews. (2 Kings 16:6, 18:26,28)
When God miraculously led these Israelites out of Egyptian bondage, and brought them to Mt. Sinai, He gave Moses a new law for the Jewish nation to set them apart from all the rest of the world. He promised to bless them and protect them as long as they would follow this law. This is the law which is known as the Mosaical Law, God's Law given through Moses, the Old Testament Law or simply the Old Law. It was designed and given only to the Israelite nation, no others. It was to last them throughout their generations until the savior had come.
You see, up until Mount Sinai, where God gave Moses the 10 commandments engraven in stone, which was not a seperate Law but the basis for their new law. The rest of the Law is recorded in the books of Leviticus, Numbers and Deuteronomy. And most of the following books detail the problems which Israel brought upon themselves for breaking God's laws, until finally they were all taken into captivity where they were when Jesus came.
All of the nations, except Israel, continued to be under the original Patriarchal law as from the beginning. However, adherence to it was virtually unknown. Although most had left following God and were worshiping false gods, we find evidence in the New Testament of a few who were still attempting to live by it. After Jesus gave his life on the cross to establish his church, whereby one could be forgiven of their sins, both the Patriarchal and the Old Testament laws were ended. Jesus nailed the Law of Moses to the cross and established his spiritual kingdom, not only for the Jews, but for all mankind, tearing down the middle wall of partition which divided them. (Ephesians 2:14-22)
An instance or two can be found where a Gentile was struggling to follow God's Patriarchal law. The first recorded one to be baptized into the new kingdom of Christ was Cornelius and his household as described in chapter 10 of Acts. Read this account And notice how Peter and the other Jews could hardly believe that the Gentiles would be accepted by God.
So the answer is yes, the Gentiles were still subject to the Patriarchal law, plus there were some who were proselytes into the Jewish religion. But none were simply forsaken with no way to serve God. Although very few did so.