Until Kobo develop their Tardis, 2011 is a reasonable earliest support date. The Kobo eReader was first introduced in May, 2010.
And 11 years' support is much better than that of other mobile device manufacturers.
http://www.cbc.ca/technology/story/2010/03/24/kobo-ebook-rea...
Via Wikipedia: https://en.wikipedia.org/wiki/Kobo_eReader