To validate whether a year is in the future you can use the following calculation template:

var year = moment('{year_field}').format('YYYY');
var year_now = moment().format('YYYY');
if (year > year_now) {
 "The year cannot be in the future";
} else {
 "The year is correct";
}

Test it here in the calculation helper.

Alternatively, you can use the following template and set up data validation rules based on the output 1 or 2.

var year = moment('{year_field}').format('YYYY');
var year_now = moment().format('YYYY');
if (year > year_now) {
 1;
} else {
 2;
}