Can gastritis elevate globulin levels to 4.2?

No: I wouldn't focus on labs but on your overall health. This is a bit elevated but reference ranges are set so that a few percent of folks fall outside on either side. Even mild liver dysfunction, as is often seen in overweight, can raise globulins impressively. See if a return to an intense, fitness-focused lifestyle like when you were a teen helps normalize this and some other things. Best wishes