Atoms are actually of potentially different ages, but I'll get back to that. The important thing here is that it's a chunk of mineral, an arrangement of atoms, that can be confirmed to be 4.4 billion years old. There are atoms on Earth that are actually much older, as old as the Universe in fact. But there are atoms that are much younger too. For example, most commercial Helium comes from oil wells, where the alpha particles released by radioactive decay in rocks forms Helium and is trapped underground. This Helium is only a few million years old.
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Atoms are actually of potentially different ages, but I'll get back to that. The important thing here is that it's a chunk of mineral, an arrangement of atoms, that can be confirmed to be 4.4 billion years old. There are atoms on Earth that are actually much older, as old as the Universe in fact. But there are atoms that are much younger too. For example, most commercial Helium comes from oil wells, where the alpha particles released by radioactive decay in rocks forms Helium and is trapped underground. This Helium is only a few million years old.