Bird of paradise
Bird of Paradise (Strelitzias reginae) don't bloom until after they are six years old, and may not even then if their cultural preferences aren't met.
Some factors to keep in mind that can tip the scale in your favor and encourage flowering include giving it bright light with at least three or 4 hours of direct sunlight each day. They will not flower without enough light. It looks like they might not be getting that now... try moving it to a better window, and if you are able, outdoors in a shaded spot during the growing season.
Right now, it is best in an area of about 55 degrees, with only just enough water to keep the mixture from drying out completely, as this is it's winter rest period.
During the growing season, water more plentifully and apply a standard liquid fertilizer every two weeks.
About the largest pot you'll need is about 12 inches. Keeping it restricted can help it to flower earlier.