Maybe previous owner put second hand tyres on. As far as age is concerned the quality of tyres deteriorate with age. As pointed out by others the rate of degradation other than wear include material quality and storage (heat and sunlight). At low speed city driving you may be fine but at higher speeds, bumpy roads or emergency hard braking to avoid a collision you’ll be taking greater risks with the older tyre which include blow outs, poorer grips and stopping a little later.