The age of accountability is the age at which each individual becomes conscious of God and is able to understand the Gospel (Reference “Gospel”). The age varies with each individual as well as the ability to understand. For those who become God-conscious who have never heard the Gospel of Christ, God knows every single person and where they are located, and He is more than capable to reach every person with the Gospel.
God, since eternity past, has always known who will be responsive to the Gospel and who will not. Jesus Christ died for every human being who ever lived or ever will live, but only a minority will receive Him as Savior (Matthew 7:13,14).
This is sad and tragic… beyond measure.