Year	Age
1970	3.3
1971	3.4
1972	3.6
1973	3.8
1974	4
1975	4.2
1976	4.4
1977	4.6
1978	4.8
1979	5
1980	5.2
1981	5.4
1982	5.7
1983	5.9
1984	6.1
1985	6.3
1986	6.5
1987	6.8
1988	7
1989	7.2
1990	7.4
1991	7.6
1992	7.8
1993	8.1
1994	8.3
1995	8.5
1996	8.7
1997	8.9
1998	9.1
1999	9.3
2000	9.5
2001	9.7
2002	9.9
2003	10.1
2004	10.3
2005	10.5
2006	10.6
2007	10.8
2008	11
2009	11.2