One thing I know most yoga teachers can relate to is when they suggest that someone try yoga, the person responds with the fact that they aren't that flexible. Sometimes you want to respond and say that it builds flexibility, and sometimes you wonder if they are just trying to be polite and side step the issue of saying no thanks.
However, for those that are on the fence about yoga, and feel that some of what is holding you back is flexibility, I want to assure you that you will build flexibility, as well as strength as you practice more. It's very easy to believe that all yogis are thin, flexible, vegan, spiritual beings. I'm here to tell you that isn't completely true.
We all are human. We practice yoga for a reason. When I first started I couldn't get my glutes down on the ground in One-Legged King Pigeon. Now, I am there most of the time, unless I haven't practiced that pose in a while, or I'm stressing too much about life.
Over time, I have built up that flexibility as well as a lot of strength. At the beginning, when I tried to hold plank, I would be there for a second before dropping down to my knees to make it easier. Then I was able to hold it longer, but wasn't able to lower down to my belly without dropping to my knees first. Just recently I was surprised when I lowered down to my belly without any modifications.
It just takes time, practice, and patience. I don't want anyone to feel like they can't do something that they want to try. So don't let your belief in your flexibility or lack there-of keep you from trying something new.