This is true however a youngster cannot be a youngster for ever.
Chambers for example is 23 (I am learning a lot today on player's ages). He has been around the club for years, had his loan spell for experience, came back and done well / okay. He is surely now ready to play.
Mustafi would probably have a higher market value. Must be some fúckers out there without Sky.
I'd keep Chambers if it was my choice. I would sell Mustafi.......and Welbeck......and Perez......and Campbell. Exciting times anyway. New manager, new tactics, new keeper, new central defender, new midfield "general". I'm looking forward to a midfield three of Torreira/Xhaka/Ramsey. Probably the most balanced midfield we've had in a while.