Hi Annie--There are a few options in San Francisco for seniors. Here is one I recently covered in my blog, called The Carlisle:
There are also a few buildings that are geared toward seniors, but are predominantly 1BRs.
The Sequoias is a nice community in a central part of the city:
Please feel free to message me at firstname.lastname@example.org if you'd like to talk further. I have a Seniors Real Estate Designation and am also on the board at On Lok, a leading senior organization in San Francisco. I'd be happy to do my best to connect you to the resources you may need.