It's my understanding that Carlisle turned Edward when he was just a baby, so how, if vampires don't age, is Edward seemingly seventeen?This is...

I haven't the read the books, I admit, but I did watch the Twilight movie. In the movie, at least, Dr. Carlisle bit Edward when he looked around seventeen years old. There was a somewhat graphic flashback scene showing the moment that Edward was turned. Edward certainly wasn't a baby in that scene. The movie would probably want to stay true to the book as much as possible, and I don't imagine why they wouldn't have portrayed the turning accurately. Also, considering how vampires don't age, it makes the most sense that Edward was bitten at the age of seventeen.