Popcorn can last 6 months to a year and sometimes longer if you keep the popped popcorn sealed in a bag or in a container.
Although the popcorn loses it's freshness and taste after a few months so it's best to eat the popped popcorn within 1 to 2 months after popping the popcorn.
The popcorn will remain safe to eat well after the 2 to 3 months and even after a year but it won't be as good to eat.
After a few months the popcorn will be okay to eat but the popcorn will gradually dry out and lose flavor, so don't expect it to be fresh and tasty after a couple months.
Popcorn kernels will last up to 2 years as long as they stay in a sealed airtight container.