TT #43 · Parashas Noach · Third Aliyah · Passuk 8:21
…evil from his youth…
Torah Temimah points to R’ Yudan (defective spelling of mi-ne’urav).
English: “Evil from his youth” — R’ Yudan said: “Mi-ne’urav” is written defectively, [meaning] from the moment he is stirred and emerges into the world.
Custom (defective spelling indicating the yetzer is present from birth / early stirring).
The yetzer is present from the earliest stirring of life; practical implications include distancing from a child’s waste once he can eat a kezayit of grain.