With an app like Clear, I have 0 trouble using it and love the minimalist approach and simple interactions. I have no trouble using the app or remembering which gestures do what. Some older than me, and likely most all younger than me would feel the same way (if they use or were to use the app).
When you are analyzing it, it is easy to point out things wrong with it, but when you use it, it just feels so right.
+1 for real life user testing