He has a lump on the back of his neck, it is almost 15 years old, it was a silent pea sized lump with no pain. but he is feeling pain in it sin?

Have it checked: It's hard to evaluate such a question online, but it's possible it could be a cyst of some sort or even an enlarged lymph node or even something else. My best advice would be to have his doctor take a look at it and that way he or she would also be able to do a more thorough exam on the rest of him as well to see if there could be involvement of other parts of the body. Best wishes.