Hi Suneel,
Like Peter suggested you, you should go with that approach, but you must return array at the end. I tweaked a little bit Peter's solution with simple splitting at the end by ';' char and it worked well. Check code snippet bellow:
{%y = DateTime.now.year-50; x=DateTime.now.year; result ="Please Select;"; while (y<x) { year=++y; result+=year+";"; } return result.split(";");|(identity)GlobalAdministrator%}
Best regards,
Dragoljub