How old do you have to be to go to 24 hour fitness by yourself?

I'm 16 and my mom is going to enroll me to a 24 hour fitness but how old do i have to be in order for me to go by myself because of course im going to join the army im 5'6 or 5'7 and weigh around 199 pounds when i mean go by myself i mean without needing an adult to come with me and keep supervision on me?How old do you have to be to go to 24 hour fitness by yourself?13(: best answer(: