As a teen I worked for a farmer who had to be about 150 years old. He'd arrive at the barn with a trailer of freshly baled hay and start tossing them up into the loft. As a husky 19 yo, I'd starting out ok, but by the time the trailer is empty, I'm fighting to keep up with this guy tossing bales upwards into the loft.
He'd leave, and when he got back 40 minutes later with a new load, I had just barely finished organizing the bales, since at the end I was putting them ANYPLACE that gave me room for his next one. Then we'd repeat the process.
Until you've worked for a farmer, you have NO idea what physical labor really is. The sad part is that he's at least 50 years older than you are, and he's not even sweating.
Every teenager should do this for at least a week. This is a primer for reality!
BTW -- wear long pants and a long sleeved shirt. You will still have hay in places you didn't even know you had.
AND drink a quart of water between each load.