Legal Question in Family Law in California

First there is no such thing as a "civil union," in legal terms. There are only marriages and domestic partnerships in California. A marriage performed by a person authorized to officiate over marriages who is not a member of the clergy or other spiritual official, such as a judge or commissioner of marriages, are informally called a "civil union" sometimes, but that has no legal meaning. So you are free to get married in a "civil union." I'm guessing what you meant, though, was can you enter into a domestic partnership. California's domestic partnership law limits its application to same-sex couples and male/female couples over a certain age, I think 65, but I'd have to look it up to be sure.