Originally Posted by
ScottGem
Being a dad is more than a piece of paper. He can't legally adopt you, but you can "adopt" him. Give him a gift on father's day. Treat him as you would a father. That should be enough.
You know how they have Marriages which are legal with a marriage certificate? Well they also have common law marriages where people do all the things married people do, but they don't have a marriage certificate.
Think of him as your common law Dad. Your Dad in all aspects except for the piece of paper.
To take that one step further, why is it important for you to have the legal system recognize him as your father? It only really matters between you and him, if you want to call yourself adopted by him to your friends, go for it. If you want to consider yourself his adopted son, you certainly can.
The reason for adoption of someone younger is because they are not an adult and they need an adult to handle their affairs. You are an adult capable and legally required to handle your own affairs, hence unless you are in some way legally, mentally or physically incompetent to handle your own affairs there is no chance that another adult can make those decisions for you; nor should you give that power to another adult, ever.