The original Holy Thorn was a centre of pilgrimage in the Middle Ages but was chopped down during the English Civil War.[42] A replacement thorn was planted in the 20th century on Wearyall hill (originally in 1951 to mark the Festival of Britain; but the thorn had to be replanted the following year as the first attempt did not take).[43] Many other examples of the thorn grow throughout Glastonbury including those in the grounds of Glastonbury Abbey, St Johns Church and Chalice Well.
The article says it is 50 years old. Apparently after the first replacement one died.
Its a cutting of the original (or maybe a cutting of a cutting). I know that botanists have had a look at it and confirm that it is not native to Britain, but is of a type commonly found in the middle east.