California Age Discrimination
Not all age discrimination is illegal. The main requirement for an age discrimination case is that you be at least 40 years old. That is, if you are 30 years old, and you are fired so that you can be replaced with a 20 year old, this is perfectly legal so long as you are an at-will employee. Again, "at-will" means that you can be terminated at any time for any reason, as long as that reason is not illegal. The law only defines age discrimination as applying to people at least 40 years old, so a termination of someone younger than 40 years old can not give rise to a claim for age discrimination.
Illegal Practices
Age discrimination can take many forms, and it does not always entail the person being fired. Any type of adverse employment action that is based on your age will be illegal, including, demotion, reduction in hours, suspension, unfavorable transfer, and failing to receive a promotion.
Proving Age Discrimination
Proving age discrimination can be difficult. It is not enough that you are over 40 and they fired you. You must be able to prove that the reason they fired you is that you are over 40. If it is a large company, statistics can help to prove that the company has a policy of terminating people who are over 40, but statistics can be problematic because the company will introduce their own version of the statistics that shows how wonderfully the company treats its older employees.
A good way to prove age discrimination is through documented incidents of managers commenting on your age. Frequently, managers use words such as "dinosaurs" and "old-dogs" to describe older employees. You should document the use of these terms and complain to your HR department about them. The more documents you have, especially about complaints to HR, the better your case will be. Keep in mind that when we go to trial, we are asking that the jury believe that you were discriminated against based on your age. If you never complained about it while you were employed, it is difficult for a jury to see how it was so bad that you should be entitled to damages. Everyone is poked fun of at some point, and juries will tend to discount off-hand statements unless you took them seriously at the time. If you complained to HR and the behavior continued, it is much easier to prove that the company was ignoring the law and illegally discriminated against you.
You should note that in proving any type of age discrimination, it is important that the person replacing you be under 40. You will have a difficult case if they fire you and replace you with someone else who is also over 40. In addition, if you fail to receive a promotion, but the person who does receive the promotion is also over 40, you will not have much of a case.