Couldn't it be bunici as well as bunicii? The translation is "Grandparents are old," not "The grandparents are old."
Being a Romance language, Romanian uses the definite article to make general statements about nouns, while English uses no article:
"Grandparents (in general) are old = "Bunicii sunt bătrâni"
It should be "THE grandparents are old"
In English you don't use the article for general statements, therefore the translation is finde.
On the other hand, we kind of don't know if this really is a general statement, so it's at least arguable.
At both speeds sounds like batrui . Is that correct?