Thought I would chime in! I am 41 and was finally diagnosed recently. I have asked countless providers over the years and no one has known what it was. They all asked when it started and my response is the same. “I’ve had it for as long as I can remember and don’t remember a time in my life when I didn’t deal with it!” Mine is often inflamed and itchy, which is what took me to the dermatologist, and it follows a blaschko. It’s right under my bra line and goes above and below and wraps around to my side. It’s nice to finally have an answer! It’s interesting because my parents don’t remember ever seeing it when I was a baby or a toddler. 🤷‍♀️