do you have to be 18 to get a membership and how much a month?

Yes

Likely you do have to be 18, as that's what most real gyms require. Although PF isn't a real gym, but a cesspool of discrimination, free pizza and mediocrity coated in lite weights and purple paint. So they may take people of all ages. Unless you look like you actually lift weights. If you fit the mold however, the most expensive option is about $20 a month for their black card membership

Yes, you must be 18, unless your parents purchase it. The cost is $10.00 a month.