Is there a shelf life for seeds?

Can I take a bag of old seeds,(last year,) and make like Johnny Appleseed, or are they trash after a while?
If they are ok, when would be the best time to spread some love around?

 

After a long while they won't be good anymore, but only if they were left out to bake in the sun. If any can be easily crushed, they are no good, and if when you put them in a cup of water if they sink right away then they are no good. Otherwise it they should be ok.

 

"Can I take a bag of old seeds,(last year,) and make like Johnny Appleseed, or are they trash after a while?"
Like Hamsammich said, last years seeds should be OK, especially if they were stored halfway decent. Remember - in nature; this years plant comes from last years seed.

"If they are ok, when would be the best time to spread some love around?"
That depends on where you are located. The season is rapidly approaching for most of the U.S. You just have to wait untill the last frost of Winter has passed for your area. A special day for planters is April 20th (4-20).