The Bird is tropical, so yes, delay putting it out until you know the temperature will remain (at least) above 50. I am being conservative here, but if you shoot for the 50 low, and you have a freak cold snap that takes the temperatures down into the 40's, you'll still be OK.
Birds grow fast in the tropics but much more slowly in temperate regions. I don't know that you will ever truly be able to know its age. Why is the age important? In the tropical and sub-tropical areas, Birds are in-the-ground landscape plants. While I was in the Miami area, I saw lots of them in the landscapes. I grew them in huge pots when living on the MS Gulf Coast and had really rare, all-white ones as well as the standard oranges. The whites were absolutely gorgeous. I don't know about them liking to be pot-bound. I would just suggest you have really well-draining soil, regardless of the pot/plant size.
