Shape Shifter

So you know the toy for kids where there are holes of different shapes and blocks that are made to fit through each one?  My son has one of those..10 blocks - 2 of each shaped in a circle, triangle, square, star and plus sign.  The lid has one of each of these shapes on it.  He hasn't perfected this game yet and has trouble matching up the shapes.  I'm not sure how old you should be when you finally understand the concept behind the toy so I sometimes worry he's developmentally behind.  I typically point out where the block needs to go but even then, if you don't put the block in the exact same position as the shape of the hole, obviously it won't fit, so he generally gets frustrated and leaves it alone or gives it to me to put in.  More recently, he's been lifting off the lid when the block won't fit in the way he wants, and just throws the block directly into the container, which I find an amusing development.   It's a heck of a lot easier than trying to figure out how to make the block fit properly in the hole.  Seems like the easy way out?..Or is it really quite ingenious of him?  He's probably thinking why bother with this whole fit-in-the-hole nonsense when you can just lift the cover off and put it in the container.  Ha.