RE: monokote hinges
I can't say how old it is. It's off a 100' roll I bought used. I've had it four years, and used it with no issues on a couple other planes. Storage under my ownership has been at stable temp & humidity.
If any covering gets brittle as it gets old, then that should be worth knowing if you're thinking of flexing them thousands of times in the same exact spot.
I am not partial to either monokote or ultracote. They each have advantages and disadvantages, and I will continue to use them both until something better comes along. But for film hinges I think I'll stick to ultracote.