Do your tyres have less than 4/32 of tread depth remaining? Or are they showing signs of uneven wear, feathering, cracking or dry rot? If you can say yes to any of these factors it is time for replacement.

yes

There are time stamps on tyre walls giving produced dates. Check online or with local tyre dealer when produced. Of memory serves correctly tyres are or ought to be ok for use up to ten years but environment used in can shorten life .eg heavy sun.

Vibrations can be due to out of balance tyres . Worn joints ? Faulty dampers etc.

If tyres are vouched as within time fame for use ( we can check with manufacturers) and are low mileage with no damage? Have wheels balanced as first option. Followed by checks on car.

Yes its time for them to go :(

as my car covered only 18000 km and 41/2 years giving vibrations and troublesome driving.As approached tyre dealers they suggest to change tyres as it passed mpre than 4 years and its properties might have gone.shall i proceed