I don't believe in an age of accountability.. that is an invention of mankind.
As far as the rest, its all there in scripture. God will have mercy on whom he wants.... its his will that will be done, not ours.
FYI, we are all doomed from the moment we are conceived... it is by the grace of God that he has elected some for salvation.
Jesus chooses whom he will save, and he chooses those who believe and obey his teachings.
John 5:21 For just as the Father raises the dead and gives them life, even so the Son gives life to whom he is pleased to give it.
Who is Jesus pleased to give life? To those who obey his teachings, John 14:23.
1 Corinthians 1:27
But God chose the foolish things of the world to shame the wise; God chose the weak things of the world to shame the strong.
1 Corinthians 1:28
God chose the lowly things of this world and the despised things—and the things that are not—to nullify the things that are,
Why does God chose those things? Because the lowly things are more apt to ask for forgiveness.
2 Thessalonians 2:13
[ Stand Firm ] But we ought always to thank God for you, brothers and sisters loved by the Lord, because God chose you as firstfruits to be saved through the sanctifying work of the Spirit and through belief in the truth.
Revelation 17:14 They will wage war against the Lamb, but the Lamb will triumph over them because he is Lord of lords and King of kings—and with him will be his called, chosen and faithful followers.”
1 Thessalonians 1:4 For we know, brothers and sisters loved by God, that he has chosen you,
James 2:5 Listen, my dear brothers and sisters: Has not God chosen those who are poor in the eyes of the world to be rich in faith and to inherit the kingdom he promised those who love him?
Matthew 22:14 “For many are invited, but few are chosen.”
2 John 1:13 The children of your sister, who is chosen by God, send their greetings.
Colossians 3:12 Therefore, as God’s chosen people, holy and dearly loved, clothe yourselves with compassion, kindness, humility, gentleness and patience.