What age to switch keyboard to (digital) piano?

Hi, we are lucky enough to have both an electronic keyboard and a digital piano in our home. I'm wondering what age would be best to move my daughter to playing on the piano rather than the keyboard? She is now 4.5 years old.

Thanks

It supposed to be very gradual and natural process.
When she will be willing to try to play her pieces on piano, place the guides behind the keys and let her do it.
One day she will say: I want to play PIANO.
My students spell it out to me and I have to agree