So, this character request made be buckle down and actually do some research outside of the character themselves. Irkens are interesting.

Now Tenn here is interestingly enough a fan favorite background characters from the Invader Zim series. Before the accusations come out, Irkens don't age like humans do. The Creator never outright outlined stated how they age, but apparently all invaders are older than the oldest human. Moreover, by the time irkens become invaders, they are at adult maturity.

Why isn't this reflected in Zim? He's defective. Literally. Anyway, back into Tenn. We seen her only a handful of times, but she quickly became a fan favorite. So here, you for your choices of something pre-established, or you can choose to start from the beginning with her.