I have noticed, in my face, that sometimes a new wrinkle will pop up overnight. The first time I noticed this, I was 22. At this point it wasn't aging per se, just a muscle under the skin giving up. What surprised me was not having smile wrinkles then, but that it basically happened overnight, but when you think that what happens with the skin wrinkling is that something changes about the muscle under the skin, well, it has to happen sometime, and it might not be gradual in every case.