Hello, Kim, and Welcome to Steemit.

Re your comment about the "average age" of Steemians, for me it's great to see young kids such as yourself joining this platform. :-)

Your varied interests will most likely make you appreciate Steemit. Photography is among the most popular topics, and there are plenty of posts in most of the other topics / interests you stated. (Well, except for "Walking." But you can start that one off, and I'll be one of the first followers of that topic thread.

Below are a few basic points of advice re posting on Steemit.

1. Longer posts are more lucrative than short posts. If you make a post of 20–30 paragraphs, it's more likely to earn rewards.
2. Include some photos, images or graphs, to complement the text. (If your post is centered on photos, just reverse the words "paragraphs" and "photos" in the previous 2 sentences.
3. Make sure the text and photos are formatted properly, so that your post looks attractive and appealing.

Hope this helps for now. Good luck, and Full Steem Ahead!