My M4700 was first delivered in 1996 and has been stored indoors (reportedly by former owner and its’ condition/appearance seems to agree) and it now has a little over 600 hrs. The hoses look good, no leaks, no cracks, still very flexible.
My mid 1980s compactor/roller has it’s original hoses* and it has lived a rough life with the Tx DOT and then a couple of uncaring owners before me. My grandson left the hyd-brakes locked and determined to move the HST lever to full-forward regardless….the diesel engine strained, the hydraulics screamed… and an original 1980s hose burst and 15-20 gals of hyd-oil blew out onto the ground.
* I replaced that one hose and the other 7 or 9 35+ year-old hoses are still original…look dry and old but no cracks, no leaks and no intention by me to replace them.
Consider how hyd hoses are constructed. Similar to tires….They have an inner, synthetic-rubber liner, a braided main-structure (usually steel wires for strength but some low pressure hoses use a synthetic/polyester fabric) and then the outer sheath which is visible to the eye is merely a protective cover. Sun and mechanical damage to that outer cover will allow damage to proceed to the braid and once the braid weakens the inner-liner is no longer supported and will blow.
Sharp bends and physical pinching/kinking or stretching will damage the braid and reduce the support for the inner liner and then the hose will fail under pressure. Heat is also their enemy but most of the hoses on a tractor are not confined inside heated areas. Ozone/sunlight will damage them just like it will tires.