Adopting a child into your family is a wonderful and mutually rewarding action. It allows many who can't have children biologically to still build a family and gives an orphan all the benefits of parental care and family life. However, adoption is also a very complex legal process, and it is advisable to seek legal counsel and assistance to ensure a satisfactory end-result.
It can difficult to navigate all the regulations that apply to adoptions, and there are too many to list them all here. But here are some of the most important factors: a child 12 or older must give consent before being adopted, you can only adopt a child if he/she is 10 or more years younger than you, and you can't adopt someone who is already married.
You do not need to be married to qualify to adopt a child, though being married might help since having two parents might be seen by the court as in the best interests of the child. And there are rare exceptions to the rule of being 10 years or more older than the adoptee. The regulations for California adoptions are very extensive, and are outlined in Family Code Sections 8500 through 92340.