What do you intend to do with them, or is it just a sentimental thing? By the way, how long can you keep seeds before they are too old to plant? Is it different for different plant types? Just curious!
I hear a story that they found seeds in an Egyptian pyramid. They planted them and they germinated.
Don't know if it's true, but, here's a personal anecdote:
I bought a packet of seeds in 1996 - they were Snow Snap Peas, Betters Homes & Garden variety from Wal-Mart. Every year I plant about 20 seeds, and I get 100% germination. This year they grew to 7 feet tall before I finally topped them to force the fruit to start coming in!
I've never had a problem with old seeds, though some varieties definitely go bad.