I don't think it would harm your 1-year old Yorkie to eat the puppy kibble. Puppy food usually contains more protein etc because puppies have more energy and burn more calories. A 1-year old is still pretty active. So don't worry.
If you're concerned though, you could either feed them separately or in separate rooms? My second always wanted to steal my older Yorkie's food too. My older one is more picky and the younger one is a piggy. Haha...
With time, she learned to understand when I tell her "leave Scottie's food alone". They understand the tones of your sentences and eventually catch on to certain words.