There is no such group as "our game is for everybody" or "12+". I hear that too often... Do you think a 60-year-old male from Birmingham will play like a 14-year-old teenager from Tokio?
Also, not every person plays a game to win or to beat ultimate challenges. They just might want to relax and feel good after a stressful day at work. Or things at home might be troublesome and you want to get your mind of things. In these cases you want to success, get satisfaction, get noticed and not face too difficult challenges that put you down again.
Player might learn that the one place where things work for them is their favourite game ;)
I've worked on about 100 published games. I love strategy and FPS games, but I've worked on like 3 "strategy" games and 0 FPS titles. Most games I've done have not been for me, but for a quite different target group. But it is part of designers' skillset to be able to create games for all groups .
So who plays Tetris?
Puzzle games appeal to all ages. But Tetris has the speed element, so it maybe appeals more for the younger. Therefore we could aim for the 20-30 year olds. City building might appeal just a bit more to the male 60%-40%. We won't make a real difference to our target audience but go global.