M.R.
Listen to Krista, if he is perfectly fine in every other developmental aspect, and if he can talk about other things, don't worry about it.
If he starts to monelouge about fans, stops talking about other things, draws fans into conversations all the time, alienates other children by talking about fans and does not notice or care that they are not interested, or begins to target and corner adults to have these conversations about fans (like holding a hostage) then call a developmental peidatirican. If that happens, you will probably notice other issues too.
M.