Preclude adult secondhand decription


While reading The Catcher in the Rye, I ran into the following excerpt that befuddled me to say the least:

Through circumstances that tend to preclude adult, secondhand description, he leaves his prep school in Pennsylvania and goes underground…

Could you explain in layman’s terms what “preclude adult description” could possibly mean? That adults cannot describe the circumstances through which he left his prep school?

Thanks in advance!

prevent a reasonable, rational, objective description of the circumstances (probably because they are so weird).

I see,
Thank you, MM.