the age is not abnormal, many plants are technically immortal. They only die of predators, disease or changing environmental conditions. Under good conditions many plants can live for thousands of years at least, and simple plants like seagrass are even likelier to survive.
Scientists have found grass in the tundra regions that was 10.000 years old. And than I mean individual halms of grass of 10.000 years old! There simply aren't any diseases there to kill grass, no grass eaters in that region, and the grass had to deal with cold so was extremely sturdy.
Can you give me a cite or species on that. I do occasional exhibits on nature themes and that would fit nicely in a "world records" one.