You had an idea. After getting your own measurements. You then browse on Amazon and pick some cool looking clothing to be delivered to your apartment. A few days later, your clothes arrived. You eagerly put them on and feel giddy with excitement. Now that you had age appropriate clothes, you decide that you like being a kid. Grabbing the book, you turn to the immortality spell. "Immortal." You call out in a clear voice. Just like the regress spell, you feel it take effect. You then grin widely. Taking the book, you put it into a backpack fit for your new age and after grabbing your wallet and smart phone, you head out to find someone to play with.
Heading to a nearby playground, you find a group of kids that are your current age of five. You happily join in their games and make new friends.