I'm 20 years old and dislocated my shoulder swimming. Mri indicates a bankart tear of the labrum. Is surgery necessary for me to return to weightliftg?

Most likely. Contact orthopedic surgeon specializing in shoulder arthroscopic procedures. Without seeing your MRI and examining you it is impossible to make surgical decision.
Be careful. Once you have dislocated your shoulder, it can become unstable, and you may be prone to future dislocations. An orthopedic surgeon or sports medicine doctor can evaluate your injury (by physical exam and looking at your mri) and determine what level of activity you should have and if/when surgery might be needed.