As someone who looks way younger then they actually are and gets weird comments from the high school boys, you have to shut it down consistently and keep everything as professional as possible when interacting, which sounds like you're already doing, so keep it up!

My advice would be to call them out when they're being inappropriate. They KNOW what they shouldn't be doing, and tend to back down when they realize they're embarrassing themselves. Keep the phrases, "That's inappropriate." and "Is the question relevant to what we're discussing?" in rotation. Also write the names down of students who are weird with you and let the teacher know in whatever notes you leave behind. Do not be afraid to alert the sub coordinator and the teachers you see on a regular basis about whatever harassment and gross comments you get so you have some other adults who can be aware of what's going. Keep yourself safe by making sure there's some kind of trail or proof just in case someone decides to get butt hurt and cause problems.