10 month old kitten eats our 18 month old cats food ?

Is this a dominance thing ? We have found that our kitten bullies the older cat and steaks her food ????
The elder cat U.S. Much smaller than the kitten and her fur is dryer than the kitten.
We have just bought a high quality food that I will feed to the elder cat in a separate room but for how long ??? Maybe until the kitten is a year old ?
I don't want our first cat to be stressed about eating and be scared to eat when the kitten is around.

We've just bought the Kiwi peaks tinned food and we've been feeding them Taste of The Wild biscuits for 6 months now ...... Any comments .
Thankyou