The Mint is unlocked at level 35.
This structure increases your chance to earn gold each time you collect taxes.
The success rate of your Mint is based on the level of your City Hall. Meaning a level 80 City Hall would need a level 80 Mint to have the same sucess rate as a level 40 City Hall with a level 40 Mint. If your City Hall is level 80 with a level 40 Mint, you're still 40 levels behind and will have an extremely poor success rate at getting gold through taxes. Keeping your mint at the same level as your City Hall should net you a healthy amount of gold each day, usually on average about 20g per day. If your Mint starts to fall behind in levels, you're chance of finding gold through taxes will also decrease drastically.
Level Up Priority: High.