Older doesn't always mean better. That's valid for many things in life and certainly applies to rum as well. So many factors come into play. Where is it aged, in what type of vessel, at what abv, which source material, which type of still, what bottling strength, any additives.....etc.
Unfortunately, rum consumers also have to be made aware of the fact that some producers put dubious numbers on their labels posing as age statements. Joy Spence, Appleton's master blender, walks you through the different age "systems".
She misspoke when she's talking about the first system, as the number is not the age of the oldest rum in the blend, but the youngest in that case.