Hi thal_pea,
Well to answer your question about what age can babies be tested... Well I was tested when I was 3 months old and that was nearly 40yrs ago... So I dont think that there is an ange difference...
In regards to your chest pain, I wouldnt hesitate not to see a doctor, with joint pain, I am sure that if you ask your doctor to have a X-ray done, I am sure that they wont hesitate to send to you have one done..you should also ask to have a bone density test done as well, to see if you have osteoperosis...Your joint pain could be a number of things..I'd seriously go and see my doctor about the chest pain and the joint pains...
Hope this helps..
Take care