My 6 month old cat really isn't getting it. I have even tried putting her food the other side of the cat flap and trying to coax her through it but she just runs up and down outside the door (it's a glass door so she can see straight through).
I don't remember having this problem with any of my previous cats who seemed to master it really quickly but I have a feeling this one's not as bright!
I used to tape the catflap open and gradually lower how much it was open by over a few days until the cats got the idea they had to push it with their paws or noses to open it! Sounds crazy but it works.
Our cat is definitely not an award winner for brainyness, but he eventually got the hang of the flap. I'm afraid it was partly down to some manhandling by DH, physically pushing kitty through the cat flap (without hurting him of course!). Once you have done that a few times, if you just leave the cat outside until it gets hungry, it will find its way in! Even the dumbest of cats seem to obtain flashes of brilliance when it comes to food Hope your cat begins to cooperate soon!