Winter Sowing Seed Exchange FAQs ~ Can I trade older seeds?
As long as your older seeds have been kept away from severe fluctuations of temperature and/or stored away from direct sunlight they'll be fine. Many seeds can last for several, several years.
What you can do is that when you post your list of seeds put a little note into your post to let the traders know how well the seeds have been cared for by being stored well, and put the collection year next to the plant name.
The other traders will know from the very beginning that they're trading for older seeds. That will be good way to post your seeds.