Year	Age
1970	3.2
1971	3.4
1972	3.6
1973	3.8
1974	4
1975	4.2
1976	4.4
1977	4.6
1978	4.8
1979	5.1
1980	5.3
1981	5.5
1982	5.8
1983	6
1984	6.3
1985	6.5
1986	6.8
1987	7.1
1988	7.3
1989	7.6
1990	7.8
1991	8.1
1992	8.3
1993	8.6
1994	8.8
1995	9
1996	9.2
1997	9.5
1998	9.7
1999	9.9
2000	10.1
2001	10.3
2002	10.5
2003	10.7
2004	10.9
2005	11.1
2006	11.2
2007	11.4
2008	11.5
2009	11.7