A 33-year-old or 37-year-old red vetiver is maturing and would almost certainly lose some of its long-term vigor and vigor-seeking capacities as it ages. It would probably not cope well with hard labor or physically arduous duties, but otherwise it should be functioning perfectly well. Any fern plant over about 35 years would die from age-related faunal neuropathy within a relatively short amount of time, but a much older fern would be in extremely good health for years or even decades after its aging.
But it all depends on the genetics of the fern. A red vetiver, which is a flowering species, would likely suffer from age-related neuropathy but only rarely in aggressive or threatening forms, so it would not be considered to be physically or mentally compromised. A flowerless, dark-green fern also called a grey vetiver that has an upright, slender structure like a gorse would probably be in pretty good health, but would also have signs of age-related neuropathy in aggressive, threatening forms.
The best way to predict which ferns will be affected by age-related neuropathy and which will be in good health is to examine the physical structure of the fern and its flower, leaves, and silvery heart shapes. Breeders can use the detailed information to accurately predict ferns that are likely to age fast, those that could be affected, and those that should be left alone for the good of them. A doctor can also tell you which ferns are aging well in your own garden if you have sensitive eyes or other physical attributes, as they can tell you which ferns have begun to decline.
The percentage of red/gray vetsumer species that will age badly, however, is truly impossible to predict accurately with any reasonable degree of accuracy. So, when considering which ferns to try to grow in your own yard, it is important to try to avoid ferns that have already experienced that fate. Any fern is good only so long as it is healthy, and if it is known to be in constant decline (or even about to experience that fate) it will be a waste of your time and your money to try to grow it. It would certainly be better to start out on plants that do not carry that effect.
However, if you want to grow some older ferns but have difficulties when your first attempt fails, it is good to try to give these ferns time to recover before you try again. If the first try goes really well and the plant takes to life and becomes actively productive, you could then go ahead and try to grow other ferns in that same environment. Over time, however, it is likely that ferns will age, be lost from cultivation, and eventually die. A bunch of young goats next to your fern garden will soon do it a world of good!