I don't know if this generation has gone on particularly long historically speaking. So I hit up Wikipedia.
First Generation (1972 to 1977) - 5 years [N/A]
Second Generation (1976 to 1984) - 8 years [7yrs]
Third Generation (1983-1992) - 9 years [4 years]
Fourth Generation (1987 to 1996) - 9 years [6 years]
Fifth Generation (1993 to 2006) - 13 years [5 years]
Sixth Generation (1998 to present) - 14 years [7 years]
Seventh Generation (2005 to present) - 7 years [6 years]
Eighth Generation (2011 to present) - 1 year [N/A]
Wikipedia bases these numbers on when the first major system launched and when last major system was discontinued. I've put the time between generation launches in brackets. So the average time a generation lasts is 9.28 years. Average time between generations is 5.83 years.
In terms of time between generations, this one hasn't gone on any longer than previous ones. In terms of lifespan for a generation, this one still has a long time to go. Though it is entering it's final stages. Mind you the PS2 saw some of its best games come out in 2005 and 2006. So I don't think this current generation is about to loose steam anytime soon.