Tremors may be caused by-overuse of caffeine, normal aging, stress, anxiety, fatigue, side effects of medications, low blood sugar levels, Parkinson’s disease, Multiple sclerosis
, Overactive thyroid, Stroke, Brain tumour or any other brain, nerve or movement disorder. It could be a part of normal aging process for your father. But it is always better to go for a check up and rule out medical conditions. Please consult a physician for a complete check up. Hope this helps you.