Electrolytic caps can last 50 years but every 10degC in temperature increase cuts life by half (it is simply drying out). It is gradual process that increases ESR (Effective Series Resistance) of capacitor up to a point where ESR is so high that capacitor is getting hot from the power losses. Thermal runaway is even possible since hot capacitor has even higher ESR that heats up capacitor further creating condition for explosion (capacitors have vent/fuse).
I would replace 10 year old cap only if it was exposed to temperature (next to tube, etc). Be careful with amplifier that was in storage for a long time (many years) since electrolyte eats up aluminium oxide that serves as isolation (lowering breakdown voltage). Voltage on capacitor builds up aluminum oxide layer again - increasing breakdown voltage but it has to be done slowly - over few days using variable transformer slowly increasing voltage in steps.
I would replace 10 year old cap only if it was exposed to temperature (next to tube, etc). Be careful with amplifier that was in storage for a long time (many years) since electrolyte eats up aluminium oxide that serves as isolation (lowering breakdown voltage). Voltage on capacitor builds up aluminum oxide layer again - increasing breakdown voltage but it has to be done slowly - over few days using variable transformer slowly increasing voltage in steps.