Question: If I am 20 and want to apply for green card for both my parents, is that possible? I live in CA and my parents have no bad record.
Answer: If you are a US citizen you can file petitions for your parents when you reach 21.
If your parents entered the US legally they may file application to adjust the status in the US when you file your immigrant visa petition for them. If they entered the US illegally they will need waiver and they will have to return to their home country to apply for immigrant visa. This will be complicated and you should retain the services of good immigration lawyer.