If a star only 2000 years old behaves like stars that are believed to be millions of years older, then maybe the stars they think are millions of years older aren't that old.
Duhuh
The theory is that the start off real fast, as I am sure you understand, and then slow down.
The extension of that is that when young, they are fast, which we see is not true for all cases, all ages. Age is a guess only, as size.
They could start off slow, build up, then way later slow down.
And I read the next post and I'll go give him credit for the answer why.