Tire usually used less than 4 years. I believe your tire is more than 5 years old. Therefore, you will see crack at side wall.
My experience is that side wall cracking can still continue use for another 2 years, until the air starts leaking.
If you are not consistent in maintaining your car, nor check your car monthly, I don't advise you to wait. I regularly check my car, so I can know the condition at all time. If you don't check regularly, then replace tire when you have time