Just to add a little ridiculousness to the theories, I noticed that in the final scenes, Rusty was wearing a particularly silverish-grey shirt :p
Can't say I actually expect it to happen, and it probably only stood out as everyone else was wearing their usual ranger-colour-coded clothes, but still, that could be quite an amusing twist to pull to say the least

We know Tyler's age now. He's 18. Confirmed. Adult ranger.