Most moles will appear in the first 20 years of your life. Around 1 in 100 babies are actually born with moles. You should know that most of the moles are not at all dangerous as they are benign. However, some are seen as a skin malformation and can lead towards melanoma, which is definitely not something that you would want to be faced with since this is a form of cancer that is quite dangerous.
People that have a lighter skin are more susceptible to the development of moles on their body. Most of them are going to be concentrated on the arms, chest and back areas. Those that have darker skin color are happier since they will have fewer moles. People do tend to have several moles by the time they reach the age of 20.