Is it common for lung cancer to spread to cervical lymph nodes, meaning higher in the neck by jaw? how common would this be for a 30 year old?

Lung cancer, depending on type may spread through the lymph nodes or through blood. First appearance of lung cancer in upper neck nodes would be usual. You may feel the nodes every couple of weeks, if any of the lymph glands doubles in size, becomes painful, ulcerates, or other nodes become enlarged, or you develop fever, or lose weight, you should see a doctor. Wish you good health!

It is relatively common for lung cancer to involve cervical lymph nodes when it becomes metastatic, it is relatively uncommon for a 30 y ear old to be affected by lung cancer, still possible. Usually a biopsy of one of the lymph nodes clarifies the origin for the inflammation in the lymph nodes.