Year	Age
1970	3.6
1971	3.8
1972	4
1973	4.2
1974	4.3
1975	4.5
1976	4.7
1977	4.9
1978	5
1979	5.2
1980	5.4
1981	5.6
1982	5.8
1983	6
1984	6.2
1985	6.4
1986	6.6
1987	6.7
1988	6.9
1989	7.1
1990	7.3
1991	7.5
1992	7.6
1993	7.8
1994	8
1995	8.2
1996	8.3
1997	8.5
1998	8.7
1999	8.8
2000	9
2001	9.1
2002	9.3
2003	9.4
2004	9.6
2005	9.7
2006	9.9
2007	10
2008	10.1
2009	10.3