Is Claw older than I was told?

by Eve
(Bangkok)

I got Claw from a GSD breeder in February.

At the time, I was told he was 2 months old and weighed about 4kg.
But his first vaccine paper (dated in January) says he was born in November last year so he was supposed to be 3 months old at the time I got him.

When I contacted the breeder, they say the date in the paper was a mistake and he was actually born in December.

Now he is 4.5 months, according to the breeder, and weighs 23.7 kg.

Is that normal or could he be 5.5 months instead of 4.5 months?