18yr old with bulging gum, like tooth is up but gum didn't break. what is it?

Incomplete eruption.: The most common area for this to occur is in the third molar or "wisdom tooth" area which is posterior to your existing molars ie farther back than your 2nd molar. The tooth has not fully erupted and if you are 18 it may not ever fully erupt. See your dentist who can determine if you have an impaction which will require extraction.

You could be right..: You may be correct if that gum bulge is located behind the other molar teeth, because the wisdom teeth typically begin to erupt around age 17-18. Other possible causes for gum swelling include infection, cysts, and tumors. Your dentist would be able to further clarify the nature of your gum swelling.