Judges Jdg 6:11–16; 1 Sam 16:1–13; Mat 20:16
If the Torah instituted firstborn privilege, the narrative repeatedly elevated the youngest. Isaac, Jacob, Joseph, Ephraim, Gideon, David. But Saul said the same thing Gideon did and was rejected. Smallness vocabulary is not the qualifier. Election is. When Jesus said 'the last will be first,' he was summarizing a pattern the canon had been running since Genesis.
Psalms 2:9
Matthew 3:2
1 Corinthians 6:9-11