How old is the Milky Way galaxy?

Answer 1

It's very difficult to define the age of the Milky Way Galaxy, but the age of the oldest star in the Galaxy yet discovered is estimated to be about 13.2 billion years.

The Universe is believed to be around 13.73 billion years old.

Not according to that theory (not really needed for this),

but the sun is about 5 billion years old (as is the whole solar system)

and Earth has an iron core - which we know came from prior stars (lots of them)

which gives us an other couple of billion years ...

so you come up with a minimum of about 10 billion years

(and a max of 13 ... which does come from "big bang calculations").