I believe that you want to remove these stalks as they take away nutrients that would otherwise be used to bulb growth. I have to do this with garlic. If they are left on, the onions will not be very large.

I too planted several onion starts last October and by this February I started having flower buds. I was advise by the company who sold me the starts to pinch them off down at the base of the plants. I had buds on my shallots and a few on the yellow and Italian red torpedoes. This is also my first year.

Onions are biennials. They bolt during their 2nd year, or if they think it is. If you get quality sets, very few of them should be bolting. If most or all your onions are bolting, I would buy from a different supplier next time.