"Is your father seventy years old?"
Translation:Vostro padre ha settant'anni?
You can't use an article before a possessive and a close family member if it's singular and unmodified: "mia madre", "la mia madrina", "la mia madre adottiva", "le mie madri". If it were "mamma" (mom/mum) it would be a little different because it can be interpreted as a modification of madre, so "mia mamma", "la mia mamma", or even "la mamma".
I'm guessing from https://dictionary.cambridge.org/us/dictionary/italian-english/di-settanta-anni and http://context.reverso.net/traduzione/italiano-inglese/settanta+anni (which has plenty of examples) that the contraction is not mandatory in Italian. Maybe Duolingo's Italian team just didn't think to include the uncontracted form?
statements and questions are written in the same way. In written sentences only question marks can indicate the difference.
As to spoken Italian you should use a tone in your voice to indicate that you are infact asking a question and not making a statement.
"Tuo padre ha settant'anni." = Your father is 70 years old. "Tuo padre ha settant'anni ?" = Is your father 70 years old?
I agree with that. We're not mind readers. How are we supposed to know it's plural? I hope they read these posts at 'Duolingo' because this happens all the time on this app. They won't accept other correct responses because they somehow expect you to know what they want you to say, and that's the only answer they'll accept. It's very annoying!
Why is my "Tuo padre ha settant' anni?" seen as incorrect? How am I supposed to know we're talking plural here? Should I just automatically assume this for future reference? Please tell me because this cost me part of my bonus points and I'm pretty sure my answer is also a correct translation, but do tell me if I'm wrong...after all I'm here to learn.