If you are learning a piece on the piano, you are also learning how to learn, increasing your efficiency. Anything you learn will also be applicable to any other piece that is similar in any way, with similar patterns or techniques.
As an adult, learning is better, in some ways. All the self-discipline and motivation that you have learned from learning to do anything else is applicable here. There is no parent making you take piano lessons any more. It is all on you. Yet there need be no ego involved, either. You don't need to compare yourself to your siblings or some other kid who is more talented. You simply know that vast numbers of people are more talented, and an even more vast number doesn't play the piano at all. It simply doesn't matter.
Of course, people who want to get really good have to start as young children, but I am talking about people who play as pure amateurs. Even with us, it is good to have learned something as children, but the learning process is actually more enjoyable when you are older. The teacher knows you will have practiced and are bringing to bear your full analytic ability to each new task.