Translation:I am seventeen years old.
When to pronounce 七 as しち and when to say it as なな (or all of the numbers with multiple readings)? Can they ever be interchangeable in certain cases?
So far I've only noticed that しち is used for time, but I'm assuming there are a ton of other instances as well. It probably has to do with counters, which I've heard is a whole 'nother story.
田中さんは若いです。十七歳です。Ideally in this case, the second sentence is continuing with the implied subject of 田中さん without having to restate it. Granted, this example is a bit clumsy, but I think it helps illustrate why something like this isn't necessarily an understood "I" in all cases.
You agreed with me on this, though, so I'm more or less pointing it out for any friends at Duolingo that might be reviewing these remarks.
Japanese is a language that assumes all participants in a conversation understands the context during the conversation.
That's why your "It is 17 years old" and my "I'm 17 desu" are both correct. You might be talking about an Angora Rabbit sitting on top a child's head, while i was just talking about myself.
That's also why from time to time you find that answers to questions are short, too short sometimes.