Old seeds

I've used seeds that are a few years old and generally they're fine although there comes a point when they become less viable. I noticed the germination rates for my Little Gem lettuce were very poor last year but the packet was about 5 or 6 years old.  Similarly I planted the remainder of a packet of onion seeds last month and they've not been great but the pack must be around 4 or 5 years old.  It all depends on the variety though - parsnips don't keep particularly well - and the storage conditions will have an effect.

As mentioned a lot depends on how the seeds are stored. If left on a greenhouse shelf life will be very short.
Best way to store seeds for next year is to cram the packets into an old coffee jar ( or plastic box ) and keep in the fridge - air tight, cool and dark

nothing to lose by planting them, u can always buy some more if they dont come.