Patricia O'Connor, The Bonsai Balcony; Age of Trees.
The age of Bonsai can be a bragging right or an indication of the extensive care and work that a tree has gone through over "X" number of years. The appearance of age is what is, in my view, what is important. Bonsai are made more than grown, and a lot of what we do is to further the notion of the passing of decades through technique. Acquire a Tree based on the Tree you see before you and not on a "This Tree came over on the Mayflower story." If you like it, is always what matters at Day's end. Now, with Tree species, there are age indicators that will help you to know how old approximately that variety is, and that can be important: a) knowing what is appropriate for the cost. :b) How much pruning and what extremes can the tree be expected to tolerate.