Stick with a purely first person POV and don't skip even a second since birth since otherwise it'll come across as lazy.
Jokes aside, these things can be cleared up with broad generalizations. For example, if you are an avid hiker and the biography is about you hiking the Pacific Crest Trail, you may have a sentence towards the beginning like, "my parents took me camping and hiking as long as I can remember so when I started along the trail, I knew exactly what to do."
There's no need to dive into details about camping as a child unless it is specifically integral to what you want the reader to understand about you. Maybe a funny story or something you learned such as the story of how you learned to start a fire, or even better, a time you failed to start a fire and what you learned from it. Biographies aren't generally the length of the encyclopedia, even when written about the most interesting people to have ever lived. The small details aren't really what matters here. Choose a handful of the most important and integral parts of your life and weave them into a collection of stories. The superfluous details can be either eliminated or glossed over in a quick summery.
Autobiographies, or even biographies, about laymen aren't usually published but based on your post, I'm assuming that isn't the goal seeing as you plan to post it on CYS. I'd say one other thing to keep in mind is to be sure to establish themes. For example, every autobiography I've read has been mainly about one specific thing in that person's life. For example, struggling with addiction, what it's like to be a child actor, how different the life of a royal is. The autobiography should have a message, or something that you have experienced that other people have not, to be well received.