Transcranial magnetic stimulation (TMS) is a promising tool in the diagnosis and treatment of neurological disorders. It employs the electromagnetic induction principle to induce electric fields in the targeted areas in the brain by generating alternating magnetic fields from the TMS coil. The brain structure is complicated and varies from person to person, which renders it difficult to improve the efficacy of TMS treatment. This work presents whether gender or age an important factor impacting the induced electric field in the brain. This work presents the existence of the pattern of induced electric field strength and focality when dividing the MRI-derived head models by their age and gender. Also, the anatomical variations of head models are considered to further explore their impacts on the induced field strength and focality in the brain. This work will provide reference and support in explaining and determining TMS treatment protocols for clinical applications.