Year	Age
1970	3.2
1971	3.3
1972	3.4
1973	3.6
1974	3.7
1975	3.8
1976	4
1977	4.1
1978	4.3
1979	4.4
1980	4.6
1981	4.8
1982	5
1983	5.2
1984	5.4
1985	5.6
1986	5.8
1987	5.9
1988	6.1
1989	6.3
1990	6.5
1991	6.7
1992	6.9
1993	7.1
1994	7.2
1995	7.4
1996	7.6
1997	7.8
1998	7.9
1999	8.1
2000	8.3
2001	8.4
2002	8.6
2003	8.8
2004	8.9
2005	9.1
2006	9.2
2007	9.4
2008	9.5
2009	9.7