In the diagram there is a long branch since the age of stars was determined primarily by main-sequence stars. The very faint star to the right belong to the red and white dwarf stars. It is easy to read, that very bright star (= massive, left side <0 mag) are not particularly old.
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Because the age of stars is approximately calculated, it can happen that a star is estimated older than the universe is old (13.7 billion years).