Teens can Workout at Planet Fitness FREE - Through the Planet Fitness Teen Summer Challenge, high school teens ages 15 - 18 can work out as much as they want at any Planet Fitness location in the United States and Canada for FREE all summer long! Teens must work out at the location they sign up at and are not permitted to use other locations. Click here for more information and to find a Planet Fitness location near you where you can sign up. Teens under 18 must bring a parent/guardian to sign up. Once the parent/guardian waiver is signed for teens under 18, teens can workout alone. Students who are already 18 do not need a parent or guardian to be present during the sign-up process.