Fresh:
hideous marshmallow texture--approximately as unpleasant as Hostess Snowballs, but hideous in a different way.
One Month:
Much better. They now have some body to them.
One Year:
Chewey
Two Years:
Crunchy, like the marshmallows in Lucky Charms.

Most people like peeps best stale. Sort of like Circus Peanuts and licorice.

I had two-year-old peeps at burning man last year. I now have a peeps cellar.

There are now red valentine peeps, unfortunately, they are strawberry flavored.