It is easier to adopt a child of your spouse, because there will not be a long period of investigation and visits to your home.
Many states allow adult adoptions.
The process is much simpler, because the state is no longer concerned about the best interests of a child. Suppose after the adoption you learn that the child has mental or physical defects. But depending upon how much the agency knew and didn't tell you, you might be able to sue the agency for the expenses you will incur. This is a developing area of the law, so you should consult a lawyer familiar with the adoption laws of your state. Inc. All rights reserved.