@alicemello you can use a Java Snippet or a Column Expression node to have if, then, else conditions.
Your example adapted to the Column Expression node would look like this:
if (column("Age") >= 18 && column("Age") <= 30 &&
column("AST") >= 150 && column("AST") <= 250 &&
column("3P") >= 90 && column("3P") <= 150 &&
column("PTS") >= 800 && column("PTS") <= 1400 &&
column("TOV") >= 80 && column("TOV") <= 180) {
"G";
} else if (column("Age") >= 18 && column("Age") <= 34 && column("AST") > 250) {
"E";
} else {
"F";
}