According to the Oxford Dictionary, third molars are referred to as wisdom teeth because their common age of eruption is between 17 and 25. Aristotle explained it this way 2500 years ago!
The last teeth to come in man are molars called ‘wisdom-teeth’, which come at the age of twenty years, in the case of both sexes. Cases have been known in women upwards of eighty years old where at the very close of life the wisdom-teeth have come up, causing great pain in their coming; and cases have been known of the like phenomenon in men too. This happens, when it does happen, in the case of people where the wisdom-teeth have not come up in early years.
Aristotle, The History of Animals