Year	Age
1970	3.4
1971	3.6
1972	3.7
1973	3.9
1974	4
1975	4.2
1976	4.4
1977	4.5
1978	4.7
1979	4.9
1980	5.1
1981	5.2
1982	5.4
1983	5.6
1984	5.8
1985	5.9
1986	6.1
1987	6.3
1988	6.5
1989	6.6
1990	6.8
1991	7
1992	7.1
1993	7.3
1994	7.5
1995	7.6
1996	7.8
1997	8
1998	8.1
1999	8.3
2000	8.5
2001	8.6
2002	8.8
2003	8.9
2004	9.1
2005	9.3
2006	9.4
2007	9.6
2008	9.7
2009	9.8