Impulsivity has two types, reward-discounting (can't delay reward) and rapid response (without awareness of surroundings). Rapid response predominates in trait impulsivity, and its consequences. Biol Psychiatry. 2002 Jun 15;51(12):988-94.
Here is a method of measurement of impulsivity in troubled adolescents.
Early onset of delinquency associates with earlier onset and greater intensity of substance abuse. JAACAP, 2002, 41:386-393.