A picture of the plant would help a lot in determining its age. If you don't have access to a digital camera, somebody with a cell phone could probably take a picture of it for you and post it, too.
Great that it is growing, and enjoying where it is. New growth is always a good sign. Once the weather starts to warm, more fertilizer, and lots more water will not hurt. Any good potting soil will be fine. But keep in mind that Birds like to be pot-bound so don't pot it up until it is really crowded in the present pot.
Outside will definitely be much better for that plant, as it will surely be more humid unless you live in the desert. If you could give us a hint as to what part of the country you are in, that also might help us to help you better. I would think that even in the furthest north states you could put that plant outside before June.
