What is Twitch's age???

So my friend jokingly said something about underage anime characters on twitter and how people are weird so i went and asked "so then since rats have small lifespans and twitch is humanoid, would that make him a child?"

That literally lead to a 5 hour discussion with myself, narrowing it down to Twitch being mutated before he was even a month old and him being at least 7 years old due to the release date. In other words, it means I've made literally no progress on his actual age. If you apply TMNT logic, his age would start from when he was mutated. From that point, I have no clue if his age would be compared to that of a human (~80 years) or that of a common sewer rat (~2 years), both of which have him as either a child or an old man.

As for my evidence of him being mutated before he was even a month, a rat's teeth show it's age. The more yellow, the older it is. Twitch has a slight hint of yellow which means that he was ~25 days or less. This was checked with all his skins and model. As for the 7 years, that's due to release date, which would mean his 8th birthday is this year. I don't know his exact birthday, so I cant quite put an exact age :3

STILL THOUGH, this leaves me with 3 questions: How long ago was Twitch mutated relative to his release date? When the age is finally found out (or hinted at), do I use the time from when he was mutated till nor or from when he was born to determine the age? and Do I use a rat's lifespan or a human's lifespan for the age? (also when is his birthday could be a bonus thing. I wanna say happy birthday to the rat)

(also i had no clue where to put this so i just put this under story, sorry if it's under the wrong board)