First of all, welcome if you are new :))

And yes, appearance of McGonagall in FB breaks existing canon. She tells Umbridge in order of Phoenix which takes place in 1994-5 that she has been teaching in Hogwarts for 39 years that makes her first teaching year in Hogwarts be 1956. And Newt studies in Hogwarts in 1910s so how could be McGonagall in FB teaching newt.

I think we should wait for upcoming movies as JK Rowling will do something to make this more logical.

Edit: And yes, there is no confirmation of birth year of McGonagall.

Maybe she uses a time turner. I know it sounds pretty far fetched but there's a SCB video about that and it's quite convincing

Welcome to the wiki :)

@Ellie Romanoff of Winterfell to add to that, she worked 2 years for the ministry after finishing her education, meaning she graduated 1954 at age 17/18 (though 18 would be more likely). By that we can calculate she was probably born between September 1935 and August 1936.

@Jcm10313

This means McGonagall was just a child during Grindelwald's time.

I can make a guess that McGonagall that we saw in FB was not that Prof. Minerva McGonagall that we saw in HP series, she was some different McGonagall.

It's even more unlikely than the time turners tho. Cos McGonagall was Minerva's muggle father's last name. So there's no proof that there was a witch or wizard called McGonagall