If I'm correct, you need to be 18 years or older to sign up as a stock contributor. Meanwhile, I would recommend contacting your local photo club, who will help you to advance in your photography. For stock, you need to provide (ideally) unique content, well lit, well photographed and free of artefacts and other technical issues. You can also look for good YouTube videos. Some are terrible ones, but some are nicely done. You will find out after a short while whom to follow and whom to scrap.
You can submit pet pictures, but do not expect them to be big sellers, as there are many, many of them in the database. Your first cat portrait is not well lit in the shadow area, is noisy, out of focus or has motion blur. Your last 3 pictures won't pass because they are black and white.
If I saw them on social media, I would fave/like them all. Well, may be not the first of the bw pictures.
Good luck and see you in a year here as a stock contributor.