What is the historical reason for 18 years being the most commonly accepted age of adulthood?

Question

Most countries define the age of adulthood at 18 years. Why is this? Was there some historical precedent set in ancient Rome/Greece or something like that? Why 18 years and not some "nicer" number like 20 or 15?

Answer 1

The age 18 is identified as the age of adulthood in the Jewish Talmud relative having sound judgement to make monetary decisions as a judge.[7] Here, the Talmud says that every judgment Josiah, the sixteenth king of Judah (c. 640–609) issued from the age of eight, when he was crowned, until the age of eighteen was reversed and he returned the money to the parties whom he judged liable, due to concern that in his youth he may not have judged the cases correctly. Other Jew commentators have discussed whether age 13 or 18 is the age to make decisions in a Jewish Court.