Hmmm, strong is a word with interpretations.  If you believe you must be well muscled in order to take a yoga class, I would say this is not true.  If you mean strong in the sense that you have the drive to learn and practice - I would say Yes!

   When we see a person lift a heavy weight, we are impressed by the act and perhaps we might declare the person to be strong.  Yet let even one tiny section of one tiny nerve fiber get damaged and suddenly this same very strong person with very large muscles, is not very strong.

   Strength is not always about muscles or lifting heavy objects.  Strength as far as yoga is concerned has more to do with with the way we use our mind to make decisions, our determination to make positive change in our life and to find a pathway in which change is possible.  It may be our willingness to learn a discipline and practice that discipline in order to bring about the change we seek.

   Try to find a studio with classes that are open for beginners.  Try a few classes and see what you think.