A lot of people have random spots on their bodies like that, as long as it doesn't itch, isn't painful- doesn't change in size or symptoms, it's nothing to worry about- especially if it's been there as long as you remember. It could even be a scar or birth mark- that you don't recall or something along those lines. If it bothers you though, you can always get an opinion from a doctor who can take a look at it in person and give you a better idea.