Either the key is worn, the lock barrel is worn or the steering lock is engaged.
The last one can be solved by pulling down or pushing up one side of the steering wheel as you try to turn the key; this tales the load off the steering lock allowing it to disengage.
The only other fix is to try any spare keys which you have for the car. If they work then your main key needs to be replaced. If not then you need to have the ignition key barrel and possibly the entire steering lock assembly professionally replaced. As your car is an older model a garage may be able to permanently disable your steering lock as a cheaper fix if that's where the issue lies, but you'll then find that your insurance company will want to increase your premiums or even refuse cover. If your keys are chipped immobiliser keys then they may all need to be reprogrammed to the car as part of the repair job.
Answers & Comments
Either the key is worn, the lock barrel is worn or the steering lock is engaged.
The last one can be solved by pulling down or pushing up one side of the steering wheel as you try to turn the key; this tales the load off the steering lock allowing it to disengage.
The only other fix is to try any spare keys which you have for the car. If they work then your main key needs to be replaced. If not then you need to have the ignition key barrel and possibly the entire steering lock assembly professionally replaced. As your car is an older model a garage may be able to permanently disable your steering lock as a cheaper fix if that's where the issue lies, but you'll then find that your insurance company will want to increase your premiums or even refuse cover. If your keys are chipped immobiliser keys then they may all need to be reprogrammed to the car as part of the repair job.