I broke my arm when I was little they said it could cause future problems and it is. If my arm is locking up what does that mean?

Varies. There are multiple potential causes: malunion of fracture, growth abnormalities, post traumatic arthritis; don't hesitate to be seen for a specific diagnosis.
Not related. Bone breaks may lead to later arthritis. A locked up arm seems to be unrelated and should be evaluated by an orthopedist.