Yes this would make you a first time home owner buyer. However, please note, this would have come into effect the year that you were added as a co-owner.
I'm assuming that was 5 years ago which means you will need to file an adjustment for the taxes of that year. You won't need to adjust it for the years in between, only the year in which you were added as a co-owner
Here is an article that can help walk through how to make changes to filed taxes: https://turbotax.community.intuit.ca/replies/2647992