Can doing neck stretches or exercises break your neck?

No: Proper stretching and exercise can actually prevent neck pain if done correctly. See a licensed physical therapist or personal trainer to learn proper technique.

Neck stretches: Absolutely not as long as the stretch is in normal physiologic range of motion and no extreme force is applied.

Unlikely: It is generally good for your neck to stretching and exercises. The only way it could be a danger is if you have some rare pre-existing condition such as a collagen disorder or loss of bone density (rare in a 30 year old).