Year	Age
1970	4.4
1971	4.5
1972	4.7
1973	4.9
1974	5
1975	5.2
1976	5.3
1977	5.5
1978	5.6
1979	5.8
1980	5.9
1981	6.1
1982	6.2
1983	6.4
1984	6.5
1985	6.7
1986	6.8
1987	6.9
1988	7
1989	7.2
1990	7.3
1991	7.4
1992	7.5
1993	7.6
1994	7.8
1995	7.9
1996	8
1997	8.1
1998	8.2
1999	8.3
2000	8.5
2001	8.6
2002	8.7
2003	8.8
2004	8.9
2005	9
2006	9.1
2007	9.2
2008	9.3
2009	9.4