@danilo Not only seniors – I am not a senior yet, and I can't tell what's clickable.
Flat design isn't the only impediment: another is invisible activators that are revealed only when you do some magic swipe thing that is completely arbitrary. Far too many phones have this instead of a button now, and many operating systems hide scroll bars this way.
Then there are interfaces that cater to only one sense, generally vision: no contouring means nothing for vision-poor people to find the button.