First I would load test the battery, disconnected from the car. Age makes no difference for a battery to be defective. If battery tests out good, then have the alternator checked. Preliminary check for that would be 13.5 to 14.0 volts while engine running. To be sure alternator is good you must load test it as well. Also be sure all your connections are tight and clean.

PS Battery voltage should settle at 12.5 - 12.6 volts after sitting for a few minutes or overnight.

Keep us informed. James