My artistic director suggested that I get surgery to fix my average flexibility if I want a company contract. Yet he casts me in nice roles even as an apprentice. I don't know what to do.
Getting surgery to improve your flexibility does not work and would be a waste of your time and money. My advice is to meet with a dance medicine orthopedist. They can give you a prescription for physical therapy to work on your flexibility and provide you with a letter for your director explaining their approach.
The majority of your flexibility is out of your control and is due largely to the structure of your bones and elasticity of your muscle tissue. Other factors, like sex (females tend to be more flexible than males), age and warmer temperatures (which loosen you up), also affect your range of motion. You can improve your flexibility by a small degree through gentle, regular stretching.
Of course, if you don't feel that your director is looking out for your best interest, it might be time to audition for other companies. If he chose you to be an apprentice and perform choice roles, you must be talented.