Is there any way to extend the life of the hardener? A few
years ago, ProBed2000 hardener went bad on me. Last year, the
Devcon hardener went bad on me. They were stored in a cool
basement. I do not use a lot at a time, but it seems every
year to 2 years I am bedding a stock and hardener has gone
bad while the other is still fine.

Would it hurt/help to put the stuff in a freezer?

I think two years is a reasonable shelf life. I've had resin and hardener work quite a bit longer than that but I wouldn't trust it for anything where I was relying on its structural strength.

Hardener particularly can crystallize when cooled much below cool room temperature, at what point depends on the components. Can be un-crystallized with gentle warming, like a hot water bath. Freezing would definitely extend the shelf life but then you have the crystallizing problem.

Actually the mixed epoxy can be almost stopped dead in its tracks by freezing. For fun I "stuck" some left over mixed Acra Glas Gel in the freezer. Worked fine a few months later though I lost some pot life while it thawed.