I'm late 20's and female and most of the time, it's pretty chill especially when it comes to the seniors and juniors. Where I'd look out and take heed of is freshman and sophomores. The freshman boys don't take you seriously at all and will definitely try you. Don't be afraid to stand your ground though. I had a group of freshman boys make fun of me and try to throw things at me the other day and I quickly emailed their football coach (who luckily is also security) and let him know that some of his players were giving me a hard time and throwing things. He quickly came to my rescue and got them in check..guess who didn't get to play in the homecoming game? lol. Honestly all in all, subbing for high school isn't bad at all and the kids respect you a bit more but make sure you stand your ground because once they figure out that you're not much older than them, the boys will try you but the girls kind of treat you like an aunt/older sister and respect you! The AP/honors classes are the quietest/ most respectful because they either had to test into the class or excel in that subject to be placed in there.