Why is my prompt declined?

I supplied a woman image, which was previously generated by firefly and the prompt "make the woman younger like 15 years old" and my prompt was declinded with "One or more words may not meet User Guidelines. Try changing your prompt." This is using the firefly image 5 model. If I  use nano banana pro model, I get "can't load" error.

But if I change the prompt to "make the model 5 years younger" then it works, but the result is younger than I want.

If I change the prompt to "make the model 3 years younger", I get the error "Artist name detected, Including artist names in  your prompt does not meet our user guidelines. Try changing..."

Are these errors just generated at random?