How long can I store car paint in the can?

[J. J]

I bought some decent quality paint and primer for a 2-stage paint job that I keep putting off. How long can I store it in the can before it goes bad? It has never been opened since I bought it.

Also, once I do want to use it, will I need to take it to the hardware store and have them put it in the paint shaking machine? Or will a stir stick work just as well?

Thanks!