Do older hulls, 80's weaken? Is an older boat not as strong? Does anything happen to the fiberglass over the years? Are they not as safe in the rough water? Are they easier to break than a new hull?

Depends on where the boat was stored and how much weather got into each portion of the boat......In most cases a old boat was built real heavy, hence a nicer ride......It all depends on what boat and how it was stored over the years...

My '88 Formula F-206 is still in great shape. While I haven't had it out in true offshore conditions the area lakes can get whipped up with 3-4 footers. The hull hasn't made any complaints. No rattles or squeeks. When not in use it's stored on a trailer.

I have an 88 24' baja and it still handles the rough just fine. No stress cracks at all.

Our 1974 Checkmate 18' w Alpha 165 hull is like the day we bought it, save a few hundred dock scratches. It is heavy by today's standards, but that comes with the Checkmate sticker. The boat was under water in '81 for a week, and we've never been able to get the moisture completely out of the main beam under the windshield, so the gel coat heaves and straightens with the seasons.
Our '89 Checkmate 28' Maxxum is immaculate without any noticeable fiberglass deterioration, and we just bought it in September...

that's the real answer.. and you can throw in what type of resign was used, type of lay-up.. etc etc etc

big thing IMHO is if the boat was on a mooring or dry for it's live