Our Old Trees

My wife and I live in a 53 year old house which sits on a lot in an old neighborhood that back in the 1910's to 1920's used to be woods and farmland. Our yard now has only 3 trees, 2 in the back and one in the front. One tree is a rather young thorn tree, but there are also 2 different maples, which are mature; I became curious about what their ages might be. Looking online, I discovered some sources that showed how the age of a tree can be estimated from the outside, without chopping it down to count the rings.
Basically, you measure the circumference in inches at about the 4 foot level from the ground and divide by pi (3.14) to get the diameter. Then you multiply the result with the growth factor, which varies from one tree species to another. You also take into account whether the tree would have grown in a woods, or if it had grown by itself because stiff competition for water creates closer rings in the tree's growth.
We have a silver maple in the backyard with a growth factor of 3.0 which turns out to be approximately 85 years old. Our red maple in the front with a growth factor of 4.5 is about 100! We really have some antiques around here!

Mark
Here's the website for determining how old your trees are; http://www.learner.org/jnorth/tm/leaf/HowOld.html