Jim’s Hokkaido elms both came from Ray Nesci’s Bonsai Nursery. The larger tree was bought in 1997 and has only been in a bonsai pot since 2000, while the mini was bought in 1988, and has been a bonsai since 1989. They were probably about the same age when purchased, and possibly even grown from the same stock material.
As Jim says, in bonsai, the size of the tree doesn't necessarily indicate age, or for that matter, even quality.