Old in a seed is relative. Tree and woodland seed never ever quite go to sleep, so they need damp storage, need to be planted out for the following spring.
Vegetable seed that do prosper from drying also have variable storage success. Earlier posters encourage very dry conditions and storage away from light. All of the above may not help onion seed. Plant them as soon as you can.
Most seed have a 2 or more year shelf life.
Even rugged seed like tomato, have declining germination rates after the tenth year.
Very old, (as in) hundreds of year old seed are only viable after being blessed by the Easter Bunny.
