Can i have artherosclerosis in legs at age 20? i have leg pain when running. i ate super unhealthy for a year, did i cause this

Leg pain: You can have atherosclerosis at age 20. It is not likely however. Leg pain while running in your situation is probably from musculoskeletal abnormalities such your shoes not compensating for poor weight bearing and excess muscle strain produced in leg muscles. See a physician for evaluation, its possible you may need shoe inserts or other steps needed rather than vascular consideration.