What are symptoms of osteoporosis in a 20 yr old?

None usually. Osteoporosis typically does not have symptoms until a fracture occurs and the result will be pain. Other physical changes that occur include loss of height and a stooped posture. More importantly, 20 year old should not have osteoporosis unless caused by meds such as steroids or other medical conditions such as bone disorders, crohns, kidney disease. See a physician who specializes in osteoporosis.