Symbols can be made any size you want them to be, but that would involve a lot of work. You would have to redo all of the types, e.g., resistor, capacitor, etc., using the make new device dialog.
A far easier method would be to reduce the amount of empty space and length of connecting wires. Eagle will then scale the whole schematic accordingly, and the symbols will be proportionately larger. If you attach a .sch file, I can at least get it started for you.
John