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.
Rickets and osteomalacia are classic vitamin D deficiency diseases. In children, vitamin D deficiency causes rickets, which is a softening or weakening of the bones. In adults, vitamin D deficiency can lead to osteomalacia, which causes weak bones and muscles.