Always use a paint can opener to open the lid. DO NOT use a screwdriver or a sharp edge. This can distort the lid making it harder to properly close and seal the can later.
The life of paint also depends how you use it. You want to try your very best not to get paint into the rim of the paint can. This will harden over time, making it hard to seal the lid when it is closed.
The paint storage location is crucial for a long paint shelf-life. Paint should be protected from extreme temperatures – especially from freezing and also from direct sunlight.