Mike, Amy, Doves ....
As far as the cutoff point for the fullness of the gentiles, My opinion would be that when the Rapture occurs, the Gentiles will no longer be as "full" ever again as they were before that. Scripture bears out that population will drastically decrease during the tribulation. In the millennium it will be "God's chosen Nation of Israel" and the "Nations". That is why once a gentile is saved in the tribulation, even if unbeknownst he is of Israeli lineage, he becomes a Proselyte Jew. This also diminishes Gentiles in fulness. Acts 2 is a picture of this....the Kingdom of Heaven( millennium Kingdom) being at hand.


Acts 2:5-11
 

5 And there were dwelling at Jerusalem (Jews), devout men,( out of every nation) under heaven.

6 Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language.

7 And they were all amazed and marvelled, saying one to another, Behold, are not all these which speak Galilaeans?

8 And how hear we every man in our own tongue, wherein we were born?

9 Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judaea, and Cappadocia, in Pontus, and Asia,

10 Phrygia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and (proselytes,)

11 Cretes and Arabians, we do hear them speak in our tongues the wonderful works of God.


So we see gentiles are becoming Judaeo-Christian Jews. Next we see they are referred to as the "house of Israel" and they have "remission of sins of the past" and have all things common, and signs and wonders are done in their midst as a sign. They are saving themselves by converting to Christianity from an untoward generation( world).


Acts 2 : 36-47


36 Therefore let all the (house of Israel )know assuredly, that God hath made that same Jesus, whom ye have crucified, both Lord and Christ.

37 Now when they heard this, they were pricked in their heart, and said unto Peter and to the rest of the apostles,( Men) and brethren, what shall we do?

38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the (remission of sins), and ye shall receive the gift of the Holy Ghost.

39 For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call.

40 And with many other words did he testify and exhort, saying, Save yourselves from this( untoward generation).

41 Then they that gladly received his word were baptized: and the same day there were added unto them about three thousand souls.

42 And they continued stedfastly in the apostles' doctrine and fellowship, and in breaking of bread, and in prayers.

43 And fear came upon every soul: and many( wonders and signs) were done by the apostles.

44 And all that believed were together, and( had all things common);

45 And sold their possessions and goods, and parted them to all men, as every man had need.

46 And they, continuing daily with one accord in the temple, and breaking bread from house to house, did eat their meat with gladness and singleness of heart,

47 Praising God, and having favour with all the people. And the Lord added to the church daily such as should be saved.


Zec. 8:23

23 Thus saith the LORD of hosts; In those days it shall come to pass, that ten men shall take hold out of all languages of the nations, even shall take hold of the skirt of him that is a Jew, saying, We will go with you: for we have heard that God is with you.


Is.4 : 1

1 And in that day seven women shall take hold of one man, saying, We will eat our own bread, and wear our own apparel: only let us be called by thy name, to take away our reproach.