You may have heard enough people tell you Yoga is great and we know it's for All. But let me tell you why you may still not be ready to truly benefit from it:-

If all you're seeking is weight loss and cardio.

There is no quick fix and Surya Namaskars are not cardio. Yoga is a holistic mindful practice. It's a gradual lifestyle shift that brings about a change. If physical gain is all you want then you may consider other options first.

If you think you need to be flexible first.

Why the fuss about being flexible? The body will eventually become flexible when the mind is ready and breath combines. Flexibility is a by-product of regular practice. It's about having the right balance between strength, flexibility and mobility. Only one, won't serve any purpose.

If you think it's too boring/slow or monotonous. 

Practice shall be slow so we can really feel and be aware. What you may call monotonous is what is called practice. Repetition is important to create muscle memory and understanding. 
Starting with a restless or impatient state of mind will do no good.

If all you want to learn is cool insta-worthy poses.

Yoga is not just a physical practice. Sooner we learn the better. Sadly that is the only thing marketed. It is quite self-limiting to only work on the physical for external validation. The yoga practice should be complete not one dimensional.

If you think Shavasana is a waste of time.

It's not always about the "doing". A lot happens in the "non-doing". To be in a state of conscious relaxation is sadly a task for many. Something that should come naturally. Rest & recovery is as important as the movement.

If you're under peer/parent pressure or just picking up on a trend. 

While this may be common and might even work positively sometimes, but till you don't really have the inner need to seek change in your life, it won't help! Same patterns will keep repeating. Before you take it up, understand a little about why you're doing what you're doing. That will give you a clean state to start the work and open up to change.