An age-hardening copper alloy made of--as expressed in each case in weight %--0.4% to a maximum of 2% cobalt which is partially replaceable by nickel, 0.1% through 0.5% beryllium, optionally 0.03% through 0.5% zirconium, 0.005% through 0.1% magnesium and possibly a maximum of 0.15% of at least one element from the group including niobium, manganese, tantalum, vanadium, titanium, chromium, cerium and hafnium. The remainder is copper inclusive of production-conditioned impurities and usual processing additives. This copper alloy is used as the material for producing casting molds, in particular for the sleeves of continuous casting rolls as components of a two-roll casting installation.