Do I need sharper teeth?

For the past few weeks or so, my breakfast is usually cereal and then an apple an hour or so later.

Lately however, I'm having trouble eating apples.  Why you ask?  I can't seem to chew the skin.

I'm fine with Fuji and Pink Lady, but I bought some Gala (or maybe it was Braeburn), and just tried a Granny Smith and I can barely get the skin down.

Do I need to have my teeth sharpened or is this a problem that others have too?