What is the Oldest Religion Ever?
Islam was the religion of first human named Adam who was created by Allah from earth.
Here is practical proof that Allah created human beings by the witness of His name through newborn babies that only Allah demonstrated in the 21st century.
Witness for the Name of Allah (اللہ) by Newborn Baby #1
Witness for the Name of Allah (اللہ) by Newborn Baby #2
Witness for the Name of Allah (اللہ) by Newborn Baby #3
Thus, according to witness of newborn babies the name of God is Allah who created them in the womb of their mothers.
Therefore, in the light of Islam — all human beings are born Muslims.
Which is ultimately leading back to Prophet Adam (peace be upon him) by Allah who was created from the earth in the beginning.
Then his wife was created then human beings started to be created in the womb of a woman since that time.
Root of all human beings goes to Prophet Adam (peace be upon him) and it is a proof that first human was a Muslim as well whose religion was Islam.
It means that not just the oldest, but also original religion of real God Allah is only Islam since the time of first human that was created by Allah.