Technically, according to the revenue.ie site Year 1 for you would have been 2005, as this was the year during which you took out your mortgage, so you would be now in Year 6. However, in reality they go by the details that you entered on the TRS application form (as in the date that you made your first repayment), which in your case would have been 2006, so you would now be in Year 5.
Either way, you should now qualify for the extension of mortgage interest relief as announced in December’s Budget, & you should continue to get relief at the applicable rate until the end of 2017.