With seeds, how old is too old?

[Gormy Cuss]

5. I never throw out seeds. I try to germinate old ones in a light seed starting blend or Jiffy pellet

I add extras and wait to see what comes up. If nothing germinates the soil or pellet is added to a garden bed.
I think most on that list will germinate at a good rate except the leeks but just this year I coaxed a couple of plants out of a package of 2 or 3 year old seed, so you never know.