How can you let somebody know how infirm a tree is?
Answers: Cut it and count the ridges
Ask who planted it. Ask around and see if anyone knew when it started growing, if it wasn't planted. Call a local University Extension and find out what the growth rate for that species of tree is for the nouns you are in and bring in an estimate. Check property deeds and see when the lot the tree was within was first developed, because society tend to plant trees when they first move in. Carbon date the core, because the important part of several trees is no longer living tissue (if it's a true tree and is thick plenty to give you a fitting sample). Core it and count the rings (for trees that have rings). If it's an Ent, you can ask it.