No its probably not one of the oldest chemicals, proteins, amino acids and various ribonucleic acids are the oldest chemicals in life on earth.
DMT came later in human evolution to correspond to something in our habitat, to evolve.
Because all we know is simply life on earth there essentially is no "oldest", afterall we are just specs on a spec in a spec inside a spec filled with millions of other specs.
We could be part of a timeline that has the constant TT for totals time and earths whole existences only consists on 1/1thousand-trillionth of TT.
What you type makes me wonder if you have ever eaten shrooms before..
Its doesn't draw serotonin, in fact, psilocybin blocks serotonin from being receptive to your synapses.