I've been kayaking in the SF Bay area for over 10 years. I had to stop distance running for several reasons and after trying a few other sports I settled on kayaking.
There are several ways to try the sport - renting and going on a guided trip from places such as REI or CCK (Oakland, Redwood City) are highly recommended. The most valuable things they can teach you are:
1. How not to paddle with your shoulders.
2. How to get back into a kayak if you tip
3. Why you'll enjoy this enough to return.
4. Why you need to rent several different boats before you think of buying.
The most valuable exercises are those for flexibility - especially your hips and torso (NOT your shoulders and upper body).
There are many clubs in the SF Bay area offering a social and safe outing opportunities to one of the most endowed areas in the world (Elkhorn Slough, Ghosttown and semi-sunken WW! destroyer in the bay, beer and nachos after a 4 hour paddle - life can't get much better!