Discount brokerages require a minimum age of 18. However, you can create a sub-account under your dads name (as long as he signs some sort of consent form) and these sub-accounts don't have a minimum age requirement.
Vitamin D deficiency rickets can be caused by a lack of vitamin D in the diet, a lack of exposure to the sun, or malabsorption syndromes in which there is an inability of the intestines to adequately absorb nutrients from foods.
The most common cause of low vitamin D is lack of sun exposure. Low levels of vitamin D are a definite red flag that your good bill of health is being threatened. Vitamin D deficiency is an underlying cause of many poor health conditions, as well as a major factor contributing to the exacerbation of symptoms of other diseases. The causes of low vitamin D can be very complex, but ensuring you get enough may be easier than you think.