From what we know about their ages, I'm gonna try to make an estimation: they're teenagers, so they're in the range of 13-19. "18-19" are right on the border-line before twenty, so let's remove those numbers. That leaves us with 13-17. Let's split that, and say they're 13-15 to start off. There's about two years between Season 2 and Season 3, so, they're 15-17 in Rebooted. Assuming it's been almost a year since Rebooted by Skybound, they're about 16-18.
Nya is two years younger than Kai, Cole, and Jay, so in Skybound, she's 14-16. Lloyd is the youngest of the ninja, so let's say he's... 7-9 in the beginning, and 10-13 by Skybound. As for his physical age? Well, you can't really number physical ages now, can you? He is... adolescent. Despite his voice, he looks old enough to pass as the same age as the other ninja.
Masters of Spinjitzu-Rise of the Spinjitzu Master
Kai, Cole, and Jay: 13-15
Nya: 11-13
Lloyd: 7-9
Zane: 60s (physically around the age as the other ninja)
Rebooted-Possession
Kai, Cole, and Jay: 15-17
Nya: 13-15
Lloyd: 9-11
Zane: 60s (shiny)
Skybound onwards
Kai, Cole, and Jay: 16-18
Nya: 14-16
Lloyd: 10-13
Zane: 60s (still shiny)