Season 1:

Zane: 18 (I'm thinking his Dad died at age 60, and made Zane around age 40)

Cole: 17

Kai: 16

Jay: 16

Nya: 15

Lloyd: 12

Season 2:

Zane: 19

Cole: 17 about to be 18

Kai: 17

Jay: 16 about to be 17

Nya: 16

Lloyd: 13, turns 16

Season 3:

Zane: 20

Cole:19

Kai: 18

Jay: 18

Nya: 17

Lloyd: 17

Season 4:

Same as Season 3

Season 5:

Zane: 21

Cole: 20

Kai: 19

Jay: 18 about to turn 19

Nya: 18

Lloyd: 18

Season 6: 

Same as Season 5

Season 7:

Zane: 22

Cole: 20

Kai: 20

Jay: 19

Nya: 18

Lloyd: 18

(Not much time passed.)

Season 8:

Zane: 23

Cole: 22

Kai: 21

Jay: 20

Nya: 19

Lloyd: 19

Season 9: 

Same as Season 8

Season 10:

Same as Season 8, and 9

Season 11: 

Zane: 24

Cole: 23

Kai: 22

Jay: 21

Nya: 20

Lloyd: Just turned 20

Season 12:

Zane: 25

Cole: 24

Kai: 23

Jay: 22

Nya: 21

Lloyd: 20 about to be 21

Can't wait for Season 13!!!

I just kind of thought that these ages make sense to me. If you don't like it, then that's okay. Just thought it made sense. (And now I repeat myself...)