The OED defines an elder, simply, as the senior of two or more individuals - no age specified. 'Elder', as an adjective, conveys the same meaning. This is an interesting question. There are no standard industry answers, just as there isn't a standard label (senior, senior citizen, elderly, old, 65+, etc.)
Bake the trout for 10 minutes, then unfold the packet far enough to check the doneness. When done, trout is moist and flaky with an opaque appearance. Return the fish to the oven and continue baking if necessary. Trout usually cooks within 20 minutes, but may require up to 30 minutes, depending on the size of the fish.
Set the salmon fillet on top of the dill and sprinkle with salt and pepper. The layer of lemon and dill will add fragrance to the fish as it cooks. Bake the salmon in the oven for 25 to 30 minutes, depending on the thickness of the salmon fillet. To determine when the salmon is cooked, insert a sharp kitchen knife into the thickest part of the fillet and pull it to one side. The fish should appear cooked through and no longer be translucent.