You decided you need to test the book on someone or something before yourself. To test to see if it was safe. Could make yourself too young to say a spell or overdo it. You then spotted your 5 year old cat "Patchy" He was just hanging by the window.
"Progress" you say pointing at him while thinking "17 years old" sure enough Patchy was clearly older with grey fur, and you could tell with eyes he was going blind. Patchy obviously was confused as he was now an old cat.
"Oh my god. It worked....ok fix this. Regress" you say thinking 12 weeks.
Sure enough Patchy shrank into a kitten while mewing with his collar dangling like a hula hoop on a person. You lift him up and adore him. He was exactly like when you first adopted him.
You then...