In context, the younger son is Isra’el, the older is Judah...
Jeremiah 31:31
That is exactly the opposite of how the NT is read and understood. The NT interprets the OT, not the OT unlocking the NT as you have it. You might want to check out how our LORD and ALL of the Apostles seemed to apply the "mystery revealed" through the ministry of Jesus Christ and the Paraclete (1 Cor 2:14) to the OT passages cracking the code and showing how they all spoke of the Messiah.
The NT is the prophesy of the OT revealed.
Without 1st understanding the OT, one gets a false interpretation of the NT because one interprets the OT according to what they think the NT concludes without any knowledge as to who the characters are or what their purpose is.
Your theory tells me to pick up a novel, start reading 2/3 the way through and then write a report about the entirety of the novel by using the last 1/3 to define the characters & explain the time-line of what had happened in the 1st 2/3. Sorry, but your theory & logic contains absolutely no common sense what so ever.