What $($select all correct answers$)$ is wrong with the following code:

int age $=23$;

string name $=$ "Dave";

system.out.println$($name $+"$ is $"+$ age $+"$ years old."$)$;

There is nothing wrong with the code.

One of the variables is not declared.

There is improper String concatenation occuring.

One of the variables is being assigned a value with an inappropriate type.

One of the variables has an invalid identifier.

The println$()$ method is not being called properly.