How long did a high priest keep his office?

Reference the Biblical book of Exodus. God set Aaron, Moses' brother, to be the first High Priest of Israel. To be a High Priest, one had to be a direct descendant of Aaron as required by God and was to carry out the requirements instituted by God. The Jewish order of High Priest has ended with the Mosaic period. Jesus is now our High Priest. 20where Jesus, who went before us, has entered on our behalf. He has become a high priest forever, in the order of Melchizedek.