"Mary" is a name. Names are not translatable. Maria is the Romanian version, but still a name stays a personal name.
Would it be șaisprezece ani or șaisprezece de ani?
Saisprezece ani. "de" is only used after numbers 20 or higher :)
It had me use the former.
Since when does "are" mean "is" and not "has"? I haven't learned this; is it in another lesson?
Latin people "have" years, English are just old... Don't try to translate word by word, you are learning another language.
cough Maria cough