I’m 51, and when I was growing up and a young adult, “;-)” was the same as “:-)” except you might use it to indicate even more that you were joking, not just a light-hearted reply or something. Somewhere along the way “;-)” gained a flirty meaning that was not there previously, which I learned after a few times where I made a silly joke that got interpreted with a naughty subtext because of that emoticon. Which was frustrating, but it’s how language works. heh