If you find a german tank with a serial number 200, your best guess of the total number of tanks they have is 400.
With the same logic, we can guess that civilizations that discover nuclear power live around 150 years.
With the same logic, we can guess that civilizations that discover nuclear power live around 150 years.
When you look at civilisation with nuclear power, then sampling process had no chances to took civilisation existed for 120 years. Even if civilisation could live for 120 years. It is a different process of data generation, so the reasoning must be different.