Can i join gym as i do have lower back pain also due to spondylolisthesis?

Yes join the gym and: Exercise for core stabilization and strength as well as cardiovascular endurance training in addition to flexibility/stretching is the best thing for your back and diagnosis. Avoid rowing machine and weight lifting in terms of squats and deadlifts.

Yes with caution: You can join a gym but you should avoid exercises that can aggrevate your back and do exercises that can help. If you haven't already, you should see an orthopedist or doctor who treats back problems to learn what you should do treat your back. Treatment would depend on the degree of the spondylolisthesis. You may consider seeing a physical therapist to learn exercises.