The paint I have (bought in 2019) which is an acrylic enamel specifies a 1 year shelf life on the Data Sheet. I just painted my engine with it without problem. It's unactivated and no reducer needed.
My opinion (which may or may not be worth 2 cents) is that you'll probably be OK if the storage conditions aren't too hot. I think cold is a better storage condition.
Since you're painting the frame, which won't be seen easily, you'll likely be OK. You may have to reduce it a little more than the spec says to use the 1.3 tip. You'll get a finer spray with it, of course.
If it were me, I'd do a test panel and see how it works before committing to your actual project.
