I used a Magical Pie on This Pet and yet she doesn't appear to have aged at all.

This is the second pet I've had this happen on, as it also didn't work on this pet.

I have tried clearing my cookies, as well as re-logging (though I'm not really sure why this would matter). I hate to be a bother. I just don't understand why it's not causing them to age at all. Some help would be greatly appreciated. Thank you!

A Magical Pie increases a pet's Maturity, which is what's used to determine whether it's an Eggling, Hatchling, Adult, etc.

The "Age" on the profile page is just simply how much real life time has passed since the pet was created.