I hiked about 12.3 miles with my overnight pack to prepare for some long overnight hikes in August. It was fun! My feet hurt a little, but overall I think it went well! What I have planned in August will be about 13 miles the first day and 8 the second, but the elevation gain will be 3-4 times as much as I did today. Here's a picture from Governor Dodge State Park in Wisconsin:
I started about two years ago and love it. Even better is if there's snow and I'm wearing snowshoes. It's a great way to get away from everything, and the bigger the park the less likely your phone will work. Somewhere along the way I saw a comment that the further you get from roads, the better people are. Today I passed a group of horse riders, and one stopped to have his horse see me. The horse had never seen a backpacker, and the rider wanted him to be accustomed to someone wearing a bag and know they aren't a threat. They were lovely folks to chat with, and I hope I was able to help the horse be more comfortable. The horse's name was Buster.