Strength, flexibility and balance have to work together. There is naturally superflexible people that have no strength and need to work on becoming strong.
One skill need the others, it is not possible to work one separately from the other.
Yoga is perfect union, and part of this union is to find your own balance, strenght and flexibility.
I find that being "not flexible enough" should be your main reason to start practicing today. The only way to improve that is to keep practicing and being constant on your efforts.