Not wanting to resurrect the discussion about whether ancient churchyard yews were planted at pagan shrines or not, but this may assist with the age estimating game. Because yews do not have a single trunk, but multiple trunks, you cannot count tree rings to establish age. They grow fast when young and then slow down considerably. So girth related to age is an estimate based on what we know about the relative rates of growth or the average yew tree.

The Tree Council has issued a guide from the Charnwood Trust environmental charity. You need to measure the girth of your yew at about four feet from the ground. So get a long tape meaure or length of rope! Then consult this chart which I have extracted to apply only to those trees old enough to interest TMA.

Girth in feet (cms)..Estimated age
27 (823)...................1,800 years
30 (914)...................2,400 "
33 (1006)..................3,000 "
35 (1067)..................4,400 "
36 (1097)..................5,600 "
Over 36 feet ......Over 6,000 years old!

A TMA survey linked to nearby ancient sites might help establish the nationwide relationship of ancient yews to ritual (or other) ancient sites.