Irish yews are a sport of the bog standard yew - Taxus baccata. They are all descended from two trees found on a limestone crag in Fermanagh in the 1760s. They became popular in cultivation because they were straighter and resembled funereal cypresses and could be topiarised.

They certainly didn't exist during the longbow era, but possibly modern bowyers may prefer them to the ordinary yew. Whether "English yew was crap for making bows" or not is hardly a valid point - that WAS the yew wood that was used and with deadly affect by the largely Welsh archers.

Yews in the wild were cut and cropped for bows, those in churchyards were left alone. Some wild yews were over cropped and died. Other wild yews were removed when livestock was put into fields where they grew. That is why large venerable yews are almost always found in churchyards today. Looking at place and field names with the yew element - only 6% are near churches so it is a false assumptuion to believe that they were always associated with churches and pagan sites etc.

Oldest yews that I know of are three in Powys - Defynnog, Discoed and Llanfaredd. All exceed 35 feet in girth giving an estimated age of 4,500 years. Yews do not have a single trunk so it is not possible to establih age by counting tree rings.
Source : Flora Britannica