Year	Age
1970	3.2
1971	3.3
1972	3.5
1973	3.6
1974	3.8
1975	3.9
1976	4.1
1977	4.3
1978	4.4
1979	4.6
1980	4.8
1981	4.9
1982	5.1
1983	5.3
1984	5.4
1985	5.6
1986	5.8
1987	6
1988	6.2
1989	6.4
1990	6.6
1991	6.8
1992	7
1993	7.2
1994	7.4
1995	7.6
1996	7.7
1997	7.9
1998	8.1
1999	8.3
2000	8.5
2001	8.6
2002	8.8
2003	9
2004	9.1
2005	9.3
2006	9.4
2007	9.6
2008	9.7
2009	9.9