Yeah, I don't think so. As Harvey mentioned, Depending on if you can run the game with a lower spec system or not will be the difference that mostly determines the age rate since from studies that I just read up on while writing this post it turns out older kids 15-17 seem to have higher spec...
To be fair your art looks really inconsistent the Alien one is probably the best with Mooshroom cow one being my least favorite one due to it just looking bland. Sorry, I'm this not trying to bash on you or anything but is there a reason for this inconsistency in quality?