What is the best age to transplant a tree?

I have two baby trees: a southern pine and, I believe, some type of maple. The southern pine I got from Lowe’s a few weeks ago during their Earth Day tree giveaway. The presumed-maple is growing right up against my house in the front yard.

I have already research and found that the best time of year to transplant trees is during the fall after the leaves drop. However, I am unable to find a clear answer for the best age of the trees to transplant. I am assuming this fall (2011) would be too early, but I’m not sure if even next fall (2012) would still be too early.

The southern pine is about 8 inches tall. The maple is about 11 inches tall. They both appear to be quite healthy and thriving. I’m watering them appropriately from what info I’ve found on the internet for their tree types.

The southern pine is in a large planter’s pot, so I don’t worry about leaving it there until it’s mature enough to transplant. However, the maple is a “wild” tree in my yard, right up against my house. I am worried that if it goes too long, it will be difficult to remove it from the ground without harming it. Additionally, it is at the front of the house, inside my flower bed. That also makes me worry that when I have to remove it from the ground, I will kill the bushes that are its neighbors.

So, I guess I have two questions…

First, should I remove the maple from the ground now while it’s still small and transplant it into a large planter’s pot until it’s older?

Second, what is an appropriate tree-age to plant these trees in the ground?