Why? Would they have started school in the year you mentioned? Were the apple blossoms blooming in that season? Does the history match the character age then and now? Would your character have had those experiences? What language, style, TV or movie fits the character?
Knowing the MC’s birthdate can give you, the writer, a starting point. We’ve heard how a person is a product of their times. What may have helped shape your MC?
And then there’s the birth signs and the traits associated with them. I’m very much a Virgo. Are any of my characters a Virgo, maybe one is more suited to be a Capricorn?
While we can listen to our characters and how they develop in the page and through what we write, having a birthdate is a well of information we shouldn’t waste.
It also lends itself to storylines – of course the murder would happen at my party. What a way to celebrate a birthday. The anniversary coincided.
Would someone that age be a _____ or _____ or _____? If they’re dating someone younger, how much, does it fit the story timeline?