User blog comment:MyNameIsIzzyIEnjoyBeingFreaky/The age of our favorite charecters/@comment-21325751-20150602032106

Well, here's my thoughts on the characters ages:

Island and Action take place three days apart, and the original cast is 16

World Tour and Revenge of the Island aren't taking place far apart since the original contestants were on the boat, so since Cody turns 17, the original cast is 17 and the Revenge of the Island cast is 16

All-Stars takes place a year later, and Pahkitew Island shorlty after (since they went "Straight into a brand new season") so I believe in by the end of Pahkitew Island it's:

Original Cast: 18

Revenge of the Island Cast: 17

Pahkitew Island Cast: 16