We can play old and slower players but if we do we have to do so much deeper and counter attack more (Leicesteresque). We can't be a high press, high energy team when 3 or 4 players take longer to run 50 metres than my nan.
Koeman needs to decide what he wants to do, does he want to play his way, and if so put the players in that support that philosophy. If he wants to play the technically better players that are slower and less mobile then he needs to change the way he is asking them to play.
For the love of God just decide one way or another and don't keep mixing the two.