Does a referee have a power of duty over who plays in a game or is he there to just apply the rules of football.I ask because recently a ref (level 5)allowed an over age player to play in a junior game even though he knew before hand who this player was.When confronted by this he said that who plays is not down to him he is there to observe the rules.
The referee has no control over the eligibility of player to play in a game nor who plays on a team. This is a matter for the League authorities who will deal with any subsequent protest from the opposition.
Usually this problem lies not with eligibility but with a player playing under an assumed name which is also not the concern of the ref. Typically there would be League rules which state that a match card must be filled in and returned to the League duly completed. Once the ref has done that he has completed his task.
In some underage leagues that I am aware of, provision is made for a team photo to be taken with the agreement of the ref and is included in the competition rules. The only other scenario that i can think of is if a player is booked and he is asked for his name and give a false name, the referee can highlight that in his report that he believed that player x, who is known to him, gave an incorrect name. Again he just reports its and does not stop the player from participating.
The ref is there to ensure that the game is played according to the LotG not to decide on eligibility of players or who participates or not