What is the most important genetic factor influencing whether someone will develop osteoporosis?
age
exercise
gender
diet

I think all of these factors are genetic factor to whether someone develops osteoporosis, but age is the most common factor to cause osteoporosis. Therefore, I think its the most important.

Exercise - can help reduce the risk but its not a guarantee factor.

Gender -can be a major factor due to the higher risk in women for there smaller bones but not as constant as age.

Diet- lack of calcium intake does increase risk but this lack of calcium in the bones can also occur purely through age.

I'm not 100% but with the facts, I'm pretty sure its AGE.