Is it bad for me to take 5 deca zol if im 18?

No, if you follow the accurate procedure's included with taking 5-Deca-Zol then you will be fine, take an AI, a SERM, and a Testosterone Booster, also known as PCT's or Post Cycle Therapy, for Cycle Therapy take Milk Thistle and drink lots of Green Tea. You will be fine, though it's not recommended.