A man presents with bullous lesions on his face, armpit, and chest. He initially had them only in his mouth. They appear round and oval with serous fluid and some are "flabby." When pressure is applied to the lesion the fluid spreads laterally. A clinical diagnosis of pemphigus vulgaris (PV) is made. Which of the following is the usual age of onset for this condition?
under 10 years of age 10-20 years of age 20-40 years of age 40-60 years of age