Hashirama and Tobirama Era

We see that Hiruzen knew the First and Second Hokage personally and he died when he was roughly 69, assuming both previous Hokage were 25 years older than him; this means they would’ve died around somewhere between 45-50 years before Naruto and Sasuke’s first fight at The Valley of The End. So my question is; why is the Era of the Senju Brothers portrayed as if it was 100-plus years ago in the series especially during Shippuden.