gentiles not only represent the actual gentile, but also represent anyone outside the faith. Christians are the new (and true) jews, those outside the faith are still considered gentiles
you only need to read St. Justin Martyr and the opinions of the Early Church on the matter, they thought it possible that people like Socrates may have been saved
Didn't find a diagram I liked, but Hell is layered. There are two major parts, the outer parts (Limbo, Abraham's bosom) and Gehenna (The lake/pit of fire.) If you are mortally sinful you go to Gehenna to contemplate your sins and suffer for them. On the other hand, there are many people in the old testament that were righteous, yet they had sins that could not be forgiven, as Christ had not yet died on the cross. Because of this they went to what was called Abraham's Bosom, a natural paradise. When Christ died he did not go to Gehenna, but to Abraham's Bosom (Limbo).
If unbaptized babies don't go to heaven, they go to limbo, which is a natural paradise, for they have no sins to contemplate, as another example. Also some one like Socrates who never had any exposure to God, but instead found what God is through reason and opening his heart likely went to Limbo.