I started my Rosemary 3 years ago in a pot with a 6 inch diameter and 7 inches deep. I didn't touch it for three years. the soil was dry and probably had little nutrition from the looks of it after 3 years in the rain but it was still going somehow, though only about a foot high, and it had never flowered.
About a week ago I transplanted it to a pot with fresh soil. the new pot has a 9 inch diameter and is 8.5 inches deep. Since I did this a week ago, the plant has exploded. New branches growing super dense out of everywhere, and it has started flowering like crazy for the first time ever. I know you've gotten a lot of "it flowers when it feels like it" answers. my personal experience is that it flowers very quickly when it's suddenly happy. This plant is three years old tho, so I don't know if I'd expect it to flower the first year. I use it for cooking so I didn't even think that it may flower until it suddenly did this week. Honestly, I came into this thread to find out if if I need to pick the flowers off like I do with basil so that it doesn't go to seed then die.
Another thing I will mention while I'm here, I've read that Rosemary can't survive in less that -1 celcius. That's crap. I live in Canada, albeit victoria, witch is literally the warmest city in Canada thru the winter, but it does get down to like -10 during the night in the winter. I've never brought the thing inside. Maybe it couldn't survive the deep snow the rest of Canada gets, but we don't get snow here, just lots of rain, so it's fine. I don't even water it over the winter. It's the most hardy plant I've had.