the more specific information you can give, the better people can help you. For example what kind of seeds have you been trying, what is your soil like, how much sun does the area get, rain, what kind of temperatures have you been having there in Southern Calif. If you just bought the seeds when you planted them, then no the seeds aren't old. Many kinds of seeds are fussy to start in the ground, some more than others. Most seeds need to stay moist (but not wet) to sprout. Unless you are having a rainy spring, watering twice a week might not be enough, you may need to give them a light watering every day until they sprout. I don't know what kind of soil you planted in but your soil needs to be well loosened up before you plant, turned and hoed and raked til it's soft and crumbly, so that the plant roots can move through it and it is aerated. That's about the most help I can give without more information, but you might find it easier to get started just to buy some plants. Go to a good nursery and talk to them about what kinds of things are adapted to your hot dry climate (unless of course you are trying to do vegetable gardening, give us some clues
) We can't answer re are they getting enough sun unless we know what they are and how much sun they are getting, but lots of things do need at least 6-8 hrs sun daily.