Hey, c'mon - some of us remember 1979 like it was yesterday!!
I think the longevity of well-kept fiberglass boats should be well beyond what you and I will need to worry about. Any boat can be neglected into oblivion, regardless of it's construction. I suppose in some ways fiberglass is a relatively "new" material without enough history to project it's lifetime.
Who knows? maybe after 75 years service some of us will go down to the dock to find a skim of white dust on the water where our boat once was!
Seriously, though, I think you need to look at the condition and original build quality more than the age.
As far as blistering goes, there are degrees of severity that dictate how big a deal they might be. Some are largely cosmetic, others can affect the integrity of the hull skin. I think it's more of an issue with below-the-waterline cored hulls than with solid skin hulls. There are other threads and actual experts on this board that can fully address your concerns on that score.