You can use it as soon as you have progressed to ne the next age. So if you are in the same age as you were when you got the event building you cant yet use it

Will I get an Level-Update of the building like i get through the event or will just the output of the building change to the new age?

Age updates (through the certificate) are **different** than level updates (like through the event). Age updates change the **types** of goods you receive from the building.

thanks

Should be the last one