I don't know how long it will last but I it will surely lessen the older he gets. (LOL, I'm sure you already realize that.) Maybe you could get him into a sport or a hobby that could start him on his way to having his own "thing" that he can identlify with. My son loves baseball, domino rally building/Rube Goldberg machines and exotic sports cars. He is kind of known as the "expert" on these things among our friends and family, and he loves the notoriety and attention he gets because of his knowledge. He is 10 though, so he's older. He did discover baseball at 5 and sportscars at 4, so I guess it is possible for your son to find a favorite hobby at 6.
An easy and free suggestion is to get on youtube with him and start surfing for random videos of sports, lego builders, heavy machinery, bridges, architecture, cars, art, cooking demonstrations, singers, actors, dancers, rappers, drawing tutorials, computer animation tutorials. animals, etc. - anything you can think of - and see if he gets interested in any of these things. That is how my son got so hooked on dominoes, from watching youtube videos by a person named "flippycat." (Search that name on youtube and you will see some amazing stuff!) However, he found baseball when we signed him up for a t-ball team, and really found cars on his own from looking out the window as he was riding in my car. Sorry this is so long, I've had 4 cups of coffee this morning. Whee!