Here is a response I wrote on a thread over on the fig forum. It has more to do with cuttings than your specific question, but the answer, along with other learning opportunities (for most) is in there:

"Sexual maturity (flowers/fruit) and to a fair degree, the stage of genetic vigor, are determined by the ontogenetic (not chronologic) age of tree organs. We tend to think of the age of plants in the same manner we think of age in humans or animals - chronologically. We, like plants, go through several life stages - embryonic, juvenile, adolescent (intermediate in plants), and mature, are stages roughly mirrored in plants. Where we vary greatly is in the way our cells age. In animals, body cells all mature at approximately the same speed. Plants grow by consecutive divisions of cells at the growing points (meristems), so their various parts are different ages (the top of the plant is younger than the basal portion, chronologically). So, if the plant has reached a sufficient age to have mature tissues (think of it as a certain number of cell divisions), vegetative cloning can occur from 3 of the 4 phases I listed above (embryonic excluded for the purpose of what I'm talking about). So, the age of cloned plants is not the chronological age of the parent plant, rather, it is the age (or phase if you will) of the portion of the plant from which the cutting was taken.

To further confuse you, dormant buds retain the ontogenetic age of their origin. In plants, the more times a cell has to divide to make the tissue, the older it is. This is termed the ontogenetic age and the most recently formed tissue is the oldest, ontogenetically speaking.

With this in mind, imagine this: Take a cutting from the basal part of a plant (remember, this formed first & dormant buds retain the age of the tissue at the time they were formed, so the cutting will be immature, but vigorous) and a cutting from the upper portion (this is the older tissue). Let's imagine the cuttings strike (make roots) and begin growing at the same time. The basal cutting will take much longer to flower and fruit because it is taken from a portion of the plant that remains in juvenile phase, while the other cutting will be quick to flower/fruit, because it was taken from mature tissue..

Since juvenile cuttings are more vigorous, it's best to take cuttings from the lowest parts of the plant to help insure a high % of strikes, but fastest flower/fruit can be had by taking branch end-cuttings from upper parts of the plant, at the expense of a lower strike rate. The reason basal suckers root so readily is that they arise from dormant tissues that retain a young ontogenetic age, making them juvenile and vigorous.

The answer to your hypothetical question regarding the tree that dies back to the ground is found in the fact that new growth will arise from ontogenetically juvenile tissues & will therefore be 'young', and retain the characteristics of a young plant - no matter how old (chronologically) the plant proper is."

If you're confused, I'll sum it up in saying that two trees of the same chronologic age can have a large difference in their ontogenetic age because of growth rates and because you have pruned the plant back to more juvenile tissues when you prune. Trees planted out grow faster, so age ontogenetically faster than slower growing trees in little pots, so in comparing trees planted out with trees in pots, we would expect that the trees in pots would lag their counterparts in the landscape by a considerable margin in reaching maturity.

Al