Hi, Thanks for writing in. In my knowledge there is no such swelling which has been consistently associated with people born between 1980 to 2000. It will help to know specific details on the location, size and how fast it has been growing. Bony swellings over the back of the head need not necessarily be bone or arise from the inside. A lot of such swellings are firm enough to give a bony feeling and are usually benign swellings which can be called cysts. There are many types of cysts in the scalp like dermoid cyst, epidermoid cyst or sebaceous cyst. Please consult your doctor to know the probability of the swelling being a cyst or anything else. A CT scan brain might be required to characterize the swelling and know if it needs any immediate treatment. Please do not worry.