What is the approximate age of a star cluster where the brightest main sequence stars are G stars?

Question

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The approximate age of a star cluster where the brightest main sequence stars are G stars is about 10 billion years. This is because G stars, like our Sun, have a main sequence lifetime of roughly 10 billion years. As the most massive and brightest stars die off first, the presence of G stars as the brightest main sequence stars indicates that the more massive stars have already evolved off the main sequence, suggesting an age of around 10 billion years.

What Is the Approximate Age of a Star Cluster Where