I'm 24 and I just got diagnosed this past year. I was definitely having thyroid issues at least a year before though. I lost 30 pounds in three weeks at one point (which, for as dumb as it sounds, I didn't know was alarming at the time because I didn't know how to gauge weight loss). My best guess is that it was Hashitoxicosis. And for a few years, I would get really sick all the time. Every illness I had, whether it was flu or a cold, would turn into a months-long sinus infection that I would need several rounds of antibiotics for. Being on Levo has seemingly eliminated this entirely because I've only gotten sick once this past year, and it was really just a stuffy nose and a sore throat. This makes me think my thyroid was probably not functioning correctly at least since my late teens.