Depends on the neighborhood. Most of the urban core of the Bay Area dates to somewhere between the 1920s and 50s. The suburban stuff (a.k.a. everything else) maybe thirty-odd years later, and there was another wave after shuttered military bases started getting redeveloped. In Oakland, the building I'm in was built in the early 2010s. In Marin, Hamilton AFB got a bunch of tract housing in the late 90s. Treasure Island and the BVHP Navy Yard in San Francisco are still under development.
Per the wiki article (since I'm too lazy to go to the library), California was first in the nation with energy efficiency standards in 1974 and currently has the lowest energy consumption per capita in the United States. However lax things were in the early 80s in California, things were/are more lax in Texas.