CIA Factbook: Turkish 70-75%, Kurdish 18%, other minorities 7-12% (2008 est.) I don't see how that is mathmatically possible in only a few generations. Since Turkey does not record the number of Kurds separately as an ethnic group in their census figures, the exact numbers are really unknown.
From what I’ve read, estimates place the Kurds at become 2/5ths of the population of Turkey by 2050. So expecting them to become a majority, in, say, 3 generations (75 years) doesn’t seem all that unreasonable, especially considering that the ethnic Turkish population will rapidly begin to age over the coming decades.