I was thinking of having my AP lang and IB science teacher write me a rec, but, I heard you want teachers who have taught a long time? My ap lang teacher is teaching for the first time, will they know this, and will it hurt my application?
No it won’t hurt you. It’s the quality of the letter of rec that matters and if this teacher knows you well, then you are fine. I would suspect that an experienced teacher has the advantage of being able to say things like “the best student in my teaching career” or “one of the most insightful students I’ve ever…” A new teacher can only compare you to other students that year. But they can make up for that by showing an in-depth knowledge of you and your interests and making insightful comments. Make sure you get to know your teacher so he or she can do that.
And yes some teachers do develop reputations with some schools that see a lot of applicants from a particular school and have come to know the caliber of the students there. That teacher’s rec might carry a bit more weight. But again, it’s better to have a glowing rec from someone who knows you than a nice rec from someone who sees you as one of many good students.
It’s YOUR qualifications that matter, not that of your teacher.
First of all, check the requirement of each school you are going to apply. Some schools explicitly say they want LORs of teachers from junior/senior classes. Second, find the teacher that can write a positive and personal LOR for you. Knowing you for a longer time may or may not be helpful, knowing you deeper will be.