There is nothing in what you are saying that "proves" that the Gentiles referred to were new believers....
I already explained that many Gentile believers would have converted up to 10-15 years previously - perhaps you missed this part too?
Is seems a person should take all scriptures regarding converts into account. Beginning with the promise of a new covenant.
Jer. 31:
33 But this
shall be the covenant that I will make with the house of Israel; After those days, saith the LORD,
I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.
34 And they shall teach no more every man his neighbour, and every man his brother, saying, Know the LORD: for they shall all know me, from the least of them unto the greatest of them
, saith the LORD: for I will forgive their iniquity, and I will remember their sin no more.
Does this happen upon conversion? No!
Ex. 23:
28 And I will send hornets before thee, which shall drive out the Hivite, the Canaanite, and the Hittite, from before thee.
29 I will not drive them out from before thee in one year; lest the land become desolate, and the beast of the field multiply against thee.
30 By little and little I will drive them out from before thee, until thou be increased, and inherit the land.
I believe the Spiritual intent of this verse represents our wickedness, our traditions, the wicked thoughts in our minds which are our true enemy.
The Word which became Flesh drives these out of His people over time.
1 Pet. 1 Wherefore laying aside all malice, and all guile, and hypocrisies, and envies, and all evil speakings,
2 As newborn babes, desire the sincere milk of the word,
that ye may grow thereby:
James 1:
2 My brethren, count it all joy when ye fall into divers temptations;
3 Knowing
this, that the trying of your faith worketh patience.
4 But let patience have
her perfect work, that ye may be perfect and entire, wanting nothing.
Whoever these Gentiles were, they had not come to the place Peter and James were Spiritually. They were being taught by Peter and James, which means they had not been "converted" long enough, nor had they knowledge of our Lord sufficient enough to be teachers themselves. They had turned to God, or were turning to God depending on the bible version, but they had not come to the "unity of the Faith" yet.
Eph. 4:
13 Till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ:
14 That we
henceforth be no more children, tossed to and fro, and carried about with every wind of doctrine, by the sleight of men,
and cunning craftiness, whereby they lie in wait to deceive;
15 But speaking the truth in love, may grow up into him in all things, which is the head,
even Christ:
These Gentiles did not yet have the Word which became Flesh's Laws written on their hearts. They were still "Babes in Christ" and Peter and James knew it.
Acts. 15:
19 Wherefore my sentence is, that we trouble not them, which from among the Gentiles are turned to God:
20 But that we write unto them, that they abstain from pollutions of idols, and
from fornication, and
from things strangled, and
from blood.
21 For Moses of old time hath in every city them that preach him, being read in the synagogues every sabbath day.
James gave these young Christians the same instructions that Jesus gave to them.
Matt. 23:
1 Then spake Jesus to the multitude, and to his disciples,
2 Saying, The scribes and the Pharisees sit in Moses' seat:
3 All therefore whatsoever they bid you observe,
that observe and do; but do not ye after their works:
for they say, and do not.
We know from study that the Mainstream Preachers of Christ's time, the Pharisees, said they taught and followed the "Law of Moses"
(For they say) but they did not teach and follow the Law of Moses.
(And do not)
Both Peter and James would have heard this teaching of the Christ and would have understood that the Preachers of their time were "
teaching for doctrines the Commandments of men", not God as they claimed. This is important to understand.
4 For
they (Not God) bind heavy burdens and grievous to be borne, and lay
them on men's shoulders (Necks); but they
themselves will not move them with one of their fingers.
So when these preachers, "who believed" came and tried to convert the Gentiles to "their" religion they called the "law of Moses" Peter knew they were trying to turn the gentiles away from the true God and towards their traditions of man.
10 Now therefore
why tempt ye God,
to put a yoke upon the neck of the disciples,
which neither our fathers nor we were able to bear?
So the Apostles kept the Gentile converts, who had not matured enough to understand the dangers of the mainstream preaching of their time, (New Converts) away from the religious traditions of the Jews and towards God's Word which was read by the Scribes every Sabbath Day. Just like Jesus instructed them to do in their early walk.
These Gentiles were New Converts otherwise they would already know about God's Laws regarding "fornication" "idolatry" "and His "food Laws" which James instructed them to follow.
It seems like a foolish argument to try and teach that these Gentiles were seasoned believers given what the Bible actually says.