Are you talking about the age of the characters in the movies (Tracy in "La La Land", Lisa Arlington in "Blair Witch") or of the actress herself?

I'm talking about Callie Hernandez herself. The online listing of her age keeps changing.

In 2013, I remember looking up the full cast of the movie "Machete Kills" . Danny Trejo and Michelle Rodriguez are some of my favorite actors. I saw the name of Callie Hernandez and her year of birth was 1988, and I thought then "She is 10 years younger than Michelle, who was born in 1978, so would Callie be competing with Michelle for acting roles?" The ages of both actors were easy to remember in 2013, because Callie was then 25 years old and Michelle was 35 years old.
Three years later, in the movies "La La Land" and "Blair Witch" she was 28 (25 + 3), that's how I calculated it

Could the ages of 24 and 21 been a mistake of whomever put the information online? Like for example 24 could have been mixed up with her day of birth 24 (May).

@wonder2wonder said:

In 2013, I remember looking up the full cast of the movie "Machete Kills" . Danny Trejo and Michelle Rodriguez are some of my favorite actors. I saw the name of Callie Hernandez and her year of birth was 1988, and I thought then "She is 10 years younger than Michelle, who was born in 1978, so would Callie be competing with Michelle for acting roles?" The ages of both actors were easy to remember in 2013, because Callie was then 25 years old and Michelle was 35 years old.
Three years later, in the movies "La La Land" and "Blair Witch" she was 28 (25 + 3), that's how I calculated it

Could the ages of 24 and 21 been a mistake of whomever put the information online? Like for example 24 could have been mixed up with her day of birth 24 (May).

I think her agency (maybe even she) probably faked her age at some point last year for some reason (marketing maybe?) 24 at the time of Blair Witch's release and 21 at the time of La La Land's, and changed it back just now. She claims she's 21 here https://www.instagram.com/p/BFwK59AMLPY/?taken-by=cheap_mango&hl=en , could be a joke, though. Actors faking their age isn't a rare occurrence. Anyways, no problem. It's just an interesting tidbit.