Ummmm...it depends ;-D. Outdoor clumps can stay around for many decades. There's a massive clump down the road from me that turned forty a while back. My Mum has one in a pot that is easily a quarter century and, despite the confinement has little to no dieback. Someone posting here mentioned a treasured plant they'd had for twenty years.

Perhaps not quite as long as bristle cone pines but more than a marigold...

Wow. Is there anyway to find out how old a clivia plant is?