My daughter will be turning 4 this coming August. She's always loved looking at, playing with, and (recently) actually playing games. We used to play "with" Ghosts by putting the ghosts on our fingers, moving them around on the board, stacking them up, etc. But today I figured I'd try to actually teach her the game.
I gave her 4 blue and 4 yellows and showed her the spaces to set them up in. Then we started. I taught her that she can only move one ghost, one space. She got it immediately, but over the course of my 2 games and my wife's 2 games with her, she'd sometimes forget when she realized she needed a ghost somewhere (to block an enemy run for the exit, which she cannot see coming) and pick one up from anywhere and move it to the exit space. So we worked on that.
She readily understood that she wanted to get 4 of my blue ghosts, and the idea of capturing took a couple of examples until she got it. She also was able to understand the need to avoid my yellow ghosts.
I played "easy" in the first game and did not press my advantage, and she eventually won, capturing 4 of my blue ghosts. We played again, and she ended up capturing 4 of my yellow ghosts for a loss. She doesn't really play with any strategy (i.e. bluffing or attempting to move her blue ghost to the exit) yet, but I suspect with 10 or 15 more plays she'll really be comfortable with the game. Ages 6 to 14, whatever! It's fun for ages 3 to 31, at least!