There are no specific requirements for the car regarding age or environmental standards.
At the same time, it is important that the vehicle is registered in the same country of which the person moving for permanent residence to Belarus is a citizen.
You should also take into account the current EU sanction restrictions regarding the movement of motor vehicles, such as the ban on exporting cars to Belarus with an engine capacity exceeding 1.9 liters, a ground clearance higher than 165 mm, a value of more than 50,000 euros, etc.