Those particular hoses are a heavy duty multi-layer product with fabric layers. Tough. But then, it's often forgotten for decades and needs to be tough.
If I were to pick an age limit that's somewhat easy to remember, I would say that most hoses (engine coolant, stuffing box, fuel lines, deck fills, and of course all the various bilge and cockpit drain hoses) are due at about 20 years. The spendy exhaust hose can usually go thirty years.
Head hoses and fittings = sooner...
Except for the exhaust, we have done
all of these, over the last decade, in stages, on our '88 model.
Some looked pretty good when removed, some were cracked and showed swelling and the beginnings of deterioration, and some were brittle and overdue.
Formulate a program for replacement. Follow it. Do your boat's
major systems one at a time so as not to have too much on your plate at any one time. Check and/or replace any suspect hose clamps.
The parts are not too expensive, and the time you put in will pay dividends in the personal knowledge you gain of your yacht and your confidence in it will expand proportionately.
Opinions worth $.02, with Thursday discount.
LB
ps: requesting this group to define "normal" may be risky...