Year	Age
1970	3.8
1971	4
1972	4.2
1973	4.4
1974	4.6
1975	4.8
1976	5
1977	5.1
1978	5.3
1979	5.5
1980	5.7
1981	5.9
1982	6.1
1983	6.3
1984	6.5
1985	6.7
1986	6.8
1987	7
1988	7.1
1989	7.3
1990	7.4
1991	7.6
1992	7.7
1993	7.8
1994	8
1995	8.1
1996	8.2
1997	8.3
1998	8.5
1999	8.6
2000	8.7
2001	8.8
2002	8.9
2003	9
2004	9.1
2005	9.2
2006	9.3
2007	9.4
2008	9.5
2009	9.6