Telling someone like the person you describe to “Get a life!” is not helpful. This is a person who is in a comfort zone and won’t leave. You need to be more direct and specific.
Since he is living with you, decide what would be a good timeline for him to have his license and move out of your place. Then you talk with him seriously. It is quite possible you will have to have more than one serious conversation. He will take some poking to get out of his comfort zone, and he may not believe you at first. Be prepared to follow through with any deadlines you give him, if you do.
I can totally understand you being impatient with him and wanting him to get his own life, as you have gotten yours. Everyone is different; not everyone matures at the same rate.