Some people are born with moles (AKA congenital moles), however most are acquired after birth. The majority of moles tend to erupt during early childhood and then again around puberty. By in large, the vast majority of moles will be obvious by 30 years of age. Development of a new mole after 30 years of age (and particularly after 40 to 50 years of age) is much less common and would therefore warrant examination by a dermatologist to exclude the possibility of skin cancer. Interestingly, it is not uncommon for moles to spontaneously regress and disappear later in life.